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17 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" title="Chapter 1. "> |
17 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
18 <div class="titlepage"></div> |
18 <div class="chapter" id="ch2intro"> |
19 <div class="toc"> |
19 <div class="titlepage"> |
20 <p><b>Table of Contents</b></p> |
20 </div> |
21 <dl> |
21 <div class="toc"> |
22 <dt><span class="article"><a href="#id2580245">Basic Python</a></span></dt> |
22 <p> |
23 <dd><dl> |
23 <b> |
24 <dt><span class="section"><a href="#id2388008">1. Introduction</a></span></dt> |
24 Table of Contents |
25 <dt><span class="section"><a href="#id2631374">2. The Python Interpreter</a></span></dt> |
25 </b> |
26 <dd><dl> |
26 </p> |
27 <dt><span class="section"><a href="#id2631383">2.1. The Interactive Interpreter</a></span></dt> |
27 <dl> |
28 <dt><span class="section"><a href="#id2631556">2.2. <span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter</a></span></dt> |
28 <dt> |
29 </dl></dd> |
29 <span class="article"> |
30 <dt><span class="section"><a href="#id2631681">3. Editing and running a python file</a></span></dt> |
30 <a href="#id2809348"> |
31 <dt><span class="section"><a href="#id2631788">4. Basic Datatypes and operators in Python</a></span></dt> |
31 Basic Python |
32 <dd><dl> |
32 </a> |
33 <dt><span class="section"><a href="#id2631822">4.1. Numbers</a></span></dt> |
33 </span> |
34 <dt><span class="section"><a href="#id2631952">4.2. Variables</a></span></dt> |
34 </dt> |
35 <dt><span class="section"><a href="#id2632000">4.3. Strings</a></span></dt> |
35 <dd> |
36 <dt><span class="section"><a href="#id2632194">4.4. Boolean</a></span></dt> |
36 <dl> |
37 </dl></dd> |
37 <dt> |
38 <dt><span class="section"><a href="#id2632223">5. The <span class="strong"><strong>while</strong></span> loop</a></span></dt> |
38 <span class="section"> |
39 <dt><span class="section"><a href="#id2632260">6. The <span class="strong"><strong>if</strong></span> conditional</a></span></dt> |
39 <a href="#id2617111"> |
40 <dt><span class="section"><a href="#id2632330">7. <span class="strong"><strong>raw_input()</strong></span></a></span></dt> |
40 1. Introduction |
41 <dt><span class="section"><a href="#id2632484">8. <span class="strong"><strong>int()</strong></span> method</a></span></dt> |
41 </a> |
42 </dl></dd> |
42 </span> |
43 </dl> |
43 </dt> |
44 </div> |
44 <dt> |
45 <div class="article" title="Basic Python"> |
45 <span class="section"> |
46 <div class="titlepage"> |
46 <a href="#id2860477"> |
47 <div><div><h2 class="title"> |
47 2. The Python Interpreter |
48 <a name="id2580245"></a>Basic Python</h2></div></div> |
48 </a> |
49 <hr> |
49 </span> |
50 </div> |
50 </dt> |
51 <div class="toc"> |
51 <dd> |
52 <p><b>Table of Contents</b></p> |
52 <dl> |
53 <dl> |
53 <dt> |
54 <dt><span class="section"><a href="#id2388008">1. Introduction</a></span></dt> |
54 <span class="section"> |
55 <dt><span class="section"><a href="#id2631374">2. The Python Interpreter</a></span></dt> |
55 <a href="#id2860486"> |
56 <dd><dl> |
56 2.1. The Interactive Interpreter |
57 <dt><span class="section"><a href="#id2631383">2.1. The Interactive Interpreter</a></span></dt> |
57 </a> |
58 <dt><span class="section"><a href="#id2631556">2.2. <span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter</a></span></dt> |
58 </span> |
59 </dl></dd> |
59 </dt> |
60 <dt><span class="section"><a href="#id2631681">3. Editing and running a python file</a></span></dt> |
60 <dt> |
61 <dt><span class="section"><a href="#id2631788">4. Basic Datatypes and operators in Python</a></span></dt> |
61 <span class="section"> |
62 <dd><dl> |
62 <a href="#id2860659"> |
63 <dt><span class="section"><a href="#id2631822">4.1. Numbers</a></span></dt> |
63 2.2. |
64 <dt><span class="section"><a href="#id2631952">4.2. Variables</a></span></dt> |
64 <span class="emphasis"> |
65 <dt><span class="section"><a href="#id2632000">4.3. Strings</a></span></dt> |
65 <em> |
66 <dt><span class="section"><a href="#id2632194">4.4. Boolean</a></span></dt> |
66 ipython |
67 </dl></dd> |
67 </em> |
68 <dt><span class="section"><a href="#id2632223">5. The <span class="strong"><strong>while</strong></span> loop</a></span></dt> |
68 </span> |
69 <dt><span class="section"><a href="#id2632260">6. The <span class="strong"><strong>if</strong></span> conditional</a></span></dt> |
69 - An enhanced interactive Python interpreter |
70 <dt><span class="section"><a href="#id2632330">7. <span class="strong"><strong>raw_input()</strong></span></a></span></dt> |
70 </a> |
71 <dt><span class="section"><a href="#id2632484">8. <span class="strong"><strong>int()</strong></span> method</a></span></dt> |
71 </span> |
72 </dl> |
72 </dt> |
73 </div> |
73 </dl> |
74 <p><a name="ch2intro_1"></a>This document is intended to be handed out at the end of the workshop. It has |
74 </dd> |
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75 <dt> |
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76 <span class="section"> |
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77 <a href="#id2860784"> |
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78 3. Editing and running a python file |
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79 </a> |
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80 </span> |
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81 </dt> |
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82 <dt> |
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83 <span class="section"> |
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84 <a href="#id2860890"> |
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85 4. Basic Datatypes and operators in Python |
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86 </a> |
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87 </span> |
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88 </dt> |
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89 <dd> |
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90 <dl> |
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91 <dt> |
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92 <span class="section"> |
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93 <a href="#id2860925"> |
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94 4.1. Numbers |
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95 </a> |
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96 </span> |
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97 </dt> |
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98 <dt> |
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99 <span class="section"> |
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100 <a href="#id2861055"> |
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101 4.2. Variables |
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102 </a> |
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103 </span> |
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104 </dt> |
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105 <dt> |
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106 <span class="section"> |
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107 <a href="#id2861102"> |
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108 4.3. Strings |
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109 </a> |
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110 </span> |
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111 </dt> |
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112 <dt> |
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113 <span class="section"> |
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114 <a href="#id2861297"> |
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115 4.4. Boolean |
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116 </a> |
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117 </span> |
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118 </dt> |
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119 </dl> |
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120 </dd> |
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121 <dt> |
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122 <span class="section"> |
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123 <a href="#id2861325"> |
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124 5. The |
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125 <span class="strong"> |
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126 <strong> |
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127 while |
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128 </strong> |
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129 </span> |
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130 loop |
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131 </a> |
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132 </span> |
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133 </dt> |
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134 <dt> |
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135 <span class="section"> |
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136 <a href="#id2861363"> |
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137 6. The |
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138 <span class="strong"> |
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139 <strong> |
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140 if |
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141 </strong> |
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142 </span> |
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143 conditional |
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144 </a> |
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145 </span> |
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146 </dt> |
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147 <dt> |
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148 <span class="section"> |
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149 <a href="#id2861432"> |
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150 7. |
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151 <span class="strong"> |
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152 <strong> |
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153 raw_input() |
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154 </strong> |
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155 </span> |
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156 </a> |
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157 </span> |
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158 </dt> |
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159 <dt> |
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160 <span class="section"> |
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161 <a href="#id2861586"> |
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162 8. |
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163 <span class="strong"> |
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164 <strong> |
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165 int() |
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166 </strong> |
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167 </span> |
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168 method |
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169 </a> |
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170 </span> |
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171 </dt> |
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172 </dl> |
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173 </dd> |
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174 </dl> |
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175 </div> |
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176 <div class="article" title="Basic Python"> |
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177 <div class="titlepage"> |
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178 <div> |
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179 <div> |
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180 <h2 class="title"> |
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181 <a name="id2809348"> |
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182 </a> |
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183 Basic Python |
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184 </h2> |
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185 </div> |
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186 </div> |
|
187 <hr /> |
|
188 </div> |
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189 <div class="toc"> |
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190 <p> |
|
191 <b> |
|
192 Table of Contents |
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193 </b> |
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194 </p> |
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195 <dl> |
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196 <dt> |
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197 <span class="section"> |
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198 <a href="#id2617111"> |
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199 1. Introduction |
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200 </a> |
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201 </span> |
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202 </dt> |
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203 <dt> |
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204 <span class="section"> |
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205 <a href="#id2860477"> |
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206 2. The Python Interpreter |
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207 </a> |
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208 </span> |
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209 </dt> |
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210 <dd> |
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211 <dl> |
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212 <dt> |
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213 <span class="section"> |
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214 <a href="#id2860486"> |
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215 2.1. The Interactive Interpreter |
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216 </a> |
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217 </span> |
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218 </dt> |
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219 <dt> |
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220 <span class="section"> |
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221 <a href="#id2860659"> |
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222 2.2. |
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223 <span class="emphasis"> |
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224 <em> |
|
225 ipython |
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226 </em> |
|
227 </span> |
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228 - An enhanced interactive Python interpreter |
|
229 </a> |
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230 </span> |
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231 </dt> |
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232 </dl> |
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233 </dd> |
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234 <dt> |
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235 <span class="section"> |
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236 <a href="#id2860784"> |
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237 3. Editing and running a python file |
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238 </a> |
|
239 </span> |
|
240 </dt> |
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241 <dt> |
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242 <span class="section"> |
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243 <a href="#id2860890"> |
|
244 4. Basic Datatypes and operators in Python |
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245 </a> |
|
246 </span> |
|
247 </dt> |
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248 <dd> |
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249 <dl> |
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250 <dt> |
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251 <span class="section"> |
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252 <a href="#id2860925"> |
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253 4.1. Numbers |
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254 </a> |
|
255 </span> |
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256 </dt> |
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257 <dt> |
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258 <span class="section"> |
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259 <a href="#id2861055"> |
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260 4.2. Variables |
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261 </a> |
|
262 </span> |
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263 </dt> |
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264 <dt> |
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265 <span class="section"> |
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266 <a href="#id2861102"> |
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267 4.3. Strings |
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268 </a> |
|
269 </span> |
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270 </dt> |
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271 <dt> |
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272 <span class="section"> |
|
273 <a href="#id2861297"> |
|
274 4.4. Boolean |
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275 </a> |
|
276 </span> |
|
277 </dt> |
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278 </dl> |
|
279 </dd> |
|
280 <dt> |
|
281 <span class="section"> |
|
282 <a href="#id2861325"> |
|
283 5. The |
|
284 <span class="strong"> |
|
285 <strong> |
|
286 while |
|
287 </strong> |
|
288 </span> |
|
289 loop |
|
290 </a> |
|
291 </span> |
|
292 </dt> |
|
293 <dt> |
|
294 <span class="section"> |
|
295 <a href="#id2861363"> |
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296 6. The |
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297 <span class="strong"> |
|
298 <strong> |
|
299 if |
|
300 </strong> |
|
301 </span> |
|
302 conditional |
|
303 </a> |
|
304 </span> |
|
305 </dt> |
|
306 <dt> |
|
307 <span class="section"> |
|
308 <a href="#id2861432"> |
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309 7. |
|
310 <span class="strong"> |
|
311 <strong> |
|
312 raw_input() |
|
313 </strong> |
|
314 </span> |
|
315 </a> |
|
316 </span> |
|
317 </dt> |
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318 <dt> |
|
319 <span class="section"> |
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320 <a href="#id2861586"> |
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321 8. |
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322 <span class="strong"> |
|
323 <strong> |
|
324 int() |
|
325 </strong> |
|
326 </span> |
|
327 method |
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328 </a> |
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329 </span> |
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330 </dt> |
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331 </dl> |
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332 </div> |
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333 <p id="ch2intro_1"> |
|
334 This document is intended to be handed out at the end of the workshop. It has |
75 been designed for Engineering students who are Python beginners and have basic |
335 been designed for Engineering students who are Python beginners and have basic |
76 programming skills. The focus is on basic numerics and plotting using Python.</p>The system requirements:<div class="itemizedlist"><ul class="itemizedlist" type="*"> |
336 programming skills. The focus is on basic numerics and plotting using Python. |
77 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_2"></a>Python - version 2.5.x or newer.</p></li> |
337 </p> |
78 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_3"></a>IPython</p></li> |
338 The system requirements: |
79 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_4"></a>Text editor - scite, vim, emacs or whatever you are comfortable with.</p></li> |
339 <div class="itemizedlist"> |
80 </ul></div> |
340 <ul class="itemizedlist" type="*"> |
81 <div class="section" title="1. Introduction"> |
341 <li class="listitem" style="list-style-type: *"> |
82 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
342 <p id="ch2intro_2"> |
83 <a name="id2388008"></a>1. Introduction</h2></div></div></div> |
343 Python - version 2.5.x or newer. |
84 <p><a name="ch2intro_5"></a>The Python programming language was created by a dutch named Guido van Rossum. |
344 </p> |
|
345 </li> |
|
346 <li class="listitem" style="list-style-type: *"> |
|
347 <p id="ch2intro_3"> |
|
348 IPython |
|
349 </p> |
|
350 </li> |
|
351 <li class="listitem" style="list-style-type: *"> |
|
352 <p id="ch2intro_4"> |
|
353 Text editor - scite, vim, emacs or whatever you are comfortable with. |
|
354 </p> |
|
355 </li> |
|
356 </ul> |
|
357 </div> |
|
358 <div class="section" title="1.Introduction"> |
|
359 <div class="titlepage"> |
|
360 <div> |
|
361 <div> |
|
362 <h2 class="title" style="clear: both"> |
|
363 <a name="id2617111"> |
|
364 </a> |
|
365 1.Introduction |
|
366 </h2> |
|
367 </div> |
|
368 </div> |
|
369 </div> |
|
370 <p id="ch2intro_5"> |
|
371 The Python programming language was created by a dutch named Guido van Rossum. |
85 The idea of Python was conceived in December 1989. The name Python has nothing |
372 The idea of Python was conceived in December 1989. The name Python has nothing |
86 to do with the reptilian, but its been named after the 70s comedy series |
373 to do with the reptilian, but its been named after the 70s comedy series |
87 "Monty Python's Flying Circus", since it happens to be Guido's favourite |
374 "Monty Python's Flying Circus", since it happens to be Guido's favourite |
88 TV series.</p> |
375 TV series. |
89 <p><a name="ch2intro_6"></a>Current stable version of Python is 2.6.x, although Python 3.0 is also the stable |
376 </p> |
|
377 <p id="ch2intro_6"> |
|
378 Current stable version of Python is 2.6.x, although Python 3.0 is also the stable |
90 version, it is not backwards compatible with the previous versions and is hence |
379 version, it is not backwards compatible with the previous versions and is hence |
91 not entirely popular at the moment. This material will focus on the 2.6.x series.</p> |
380 not entirely popular at the moment. This material will focus on the 2.6.x series. |
92 <p><a name="ch2intro_7"></a>Python is licensed under the Python Software Foundation License (PSF License) |
381 </p> |
|
382 <p id="ch2intro_7"> |
|
383 Python is licensed under the Python Software Foundation License (PSF License) |
93 which is GPL compatible Free Software license (excepting license version 1.6 and 2.0) |
384 which is GPL compatible Free Software license (excepting license version 1.6 and 2.0) |
94 It is a no strings attached license, which means the source code is free to modify |
385 It is a no strings attached license, which means the source code is free to modify |
95 and redistribute.</p> |
386 and redistribute. |
96 <p><a name="ch2intro_8"></a>The Python docs define Python as "Python is an interpreted, object-oriented, |
387 </p> |
|
388 <p id="ch2intro_8"> |
|
389 The Python docs define Python as "Python is an interpreted, object-oriented, |
97 high-level programming language with dynamic semantics." A more detailed summary |
390 high-level programming language with dynamic semantics." A more detailed summary |
98 can be found at </p> |
391 can be found at |
99 <div class="reference"> |
392 </p> |
100 <div class="titlepage"><hr></div>http://www.python.org/doc/essays/blurb.html</div> |
393 <div class="reference"> |
101 <p>. Python is a language that |
394 <div class="titlepage"> |
|
395 <hr /> |
|
396 </div> |
|
397 http://www.python.org/doc/essays/blurb.html |
|
398 </div> |
|
399 <p> |
|
400 . Python is a language that |
102 has been designed to help the programmer concentrate on solving the problem at hand |
401 has been designed to help the programmer concentrate on solving the problem at hand |
103 and not worry about the programming language idiosyncrasies.</p> |
402 and not worry about the programming language idiosyncrasies. |
104 <p><a name="ch2intro_9"></a>Python is a highly cross platform compatible language on account of it being an |
403 </p> |
|
404 <p id="ch2intro_9"> |
|
405 Python is a highly cross platform compatible language on account of it being an |
105 interpreted language. It is highly scalable and hence has been adapted to run on |
406 interpreted language. It is highly scalable and hence has been adapted to run on |
106 the Nokia 60 series phones. Python has been designed to be readable and easy to use</p> |
407 the Nokia 60 series phones. Python has been designed to be readable and easy to use |
107 <p><a name="ch2intro_a"></a><span class="strong"><strong>Resources available for reference</strong></span></p> |
408 </p> |
108 <div class="itemizedlist"><ul class="itemizedlist" type="*"> |
409 <p id="ch2intro_a"> |
109 <li class="listitem" style="list-style-type: *"> |
410 <span class="strong"> |
110 <p><a name="ch2intro_b"></a>Web: </p> |
411 <strong> |
111 <div class="reference"> |
412 Resources available for reference |
112 <div class="titlepage"><hr></div>http://www.python.org</div> |
413 </strong> |
113 </li> |
414 </span> |
114 <li class="listitem" style="list-style-type: *"> |
415 </p> |
115 <p><a name="ch2intro_c"></a>Doc: </p> |
416 <div class="itemizedlist"> |
116 <div class="reference"> |
417 <ul class="itemizedlist" type="*"> |
117 <div class="titlepage"><hr></div>http://www.python.org/doc</div> |
418 <li class="listitem" style="list-style-type: *"> |
118 </li> |
419 <p id="ch2intro_b"> |
119 <li class="listitem" style="list-style-type: *">Free Tutorials:<div class="itemizedlist"><ul class="itemizedlist" type="*"> |
420 Web: |
120 <li class="listitem" style="list-style-type: *"> |
421 </p> |
121 <p><a name="ch2intro_d"></a>Official Python Tutorial: </p> |
422 <div class="reference"> |
122 <div class="reference"> |
423 <div class="titlepage"> |
123 <div class="titlepage"><hr></div>http://docs.python.org/tut/tut.html</div> |
424 <hr /> |
124 </li> |
425 </div> |
125 <li class="listitem" style="list-style-type: *"> |
426 http://www.python.org |
126 <p><a name="ch2intro_e"></a>Byte of Python: </p> |
427 </div> |
127 <div class="reference"> |
428 </li> |
128 <div class="titlepage"><hr></div>http://www.byteofpython.info/</div> |
429 <li class="listitem" style="list-style-type: *"> |
129 </li> |
430 <p id="ch2intro_c"> |
130 <li class="listitem" style="list-style-type: *"> |
431 Doc: |
131 <p><a name="ch2intro_f"></a>Dive into Python: </p> |
432 </p> |
132 <div class="reference"> |
433 <div class="reference"> |
133 <div class="titlepage"><hr></div>http://diveintopython.org/</div> |
434 <div class="titlepage"> |
134 </li> |
435 <hr /> |
135 </ul></div> |
436 </div> |
136 </li> |
437 http://www.python.org/doc |
137 </ul></div> |
438 </div> |
138 <p><a name="ch2intro_10"></a><span class="strong"><strong>Advantages of Python - Why Python??</strong></span></p> |
439 </li> |
139 <div class="itemizedlist"><ul class="itemizedlist" type="*"> |
440 <li class="listitem" style="list-style-type: *"> |
140 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_11"></a>Python has been designed for readability and ease of use. Its been designed in |
441 Free Tutorials: |
|
442 <div class="itemizedlist"> |
|
443 <ul class="itemizedlist" type="*"> |
|
444 <li class="listitem" style="list-style-type: *"> |
|
445 <p id="ch2intro_d"> |
|
446 Official Python Tutorial: |
|
447 </p> |
|
448 <div class="reference"> |
|
449 <div class="titlepage"> |
|
450 <hr /> |
|
451 </div> |
|
452 http://docs.python.org/tut/tut.html |
|
453 </div> |
|
454 </li> |
|
455 <li class="listitem" style="list-style-type: *"> |
|
456 <p id="ch2intro_e"> |
|
457 Byte of Python: |
|
458 </p> |
|
459 <div class="reference"> |
|
460 <div class="titlepage"> |
|
461 <hr /> |
|
462 </div> |
|
463 http://www.byteofpython.info/ |
|
464 </div> |
|
465 </li> |
|
466 <li class="listitem" style="list-style-type: *"> |
|
467 <p id="ch2intro_f"> |
|
468 Dive into Python: |
|
469 </p> |
|
470 <div class="reference"> |
|
471 <div class="titlepage"> |
|
472 <hr /> |
|
473 </div> |
|
474 http://diveintopython.org/ |
|
475 </div> |
|
476 </li> |
|
477 </ul> |
|
478 </div> |
|
479 </li> |
|
480 </ul> |
|
481 </div> |
|
482 <p id="ch2intro_10"> |
|
483 <span class="strong"> |
|
484 <strong> |
|
485 Advantages of Python - Why Python?? |
|
486 </strong> |
|
487 </span> |
|
488 </p> |
|
489 <div class="itemizedlist"> |
|
490 <ul class="itemizedlist" type="*"> |
|
491 <li class="listitem" style="list-style-type: *"> |
|
492 <p id="ch2intro_11"> |
|
493 Python has been designed for readability and ease of use. Its been designed in |
141 such a fashion that it imposes readability on the programmer. Python does away |
494 such a fashion that it imposes readability on the programmer. Python does away |
142 with the braces and the semicolons and instead implements code blocks based on |
495 with the braces and the semicolons and instead implements code blocks based on |
143 indentation, thus enhancing readability.</p></li> |
496 indentation, thus enhancing readability. |
144 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_12"></a>Python is a high level, interpreted, modular and object oriented language. |
497 </p> |
|
498 </li> |
|
499 <li class="listitem" style="list-style-type: *"> |
|
500 <p id="ch2intro_12"> |
|
501 Python is a high level, interpreted, modular and object oriented language. |
145 Python performs memory management on its own, thus the programmer need not bother |
502 Python performs memory management on its own, thus the programmer need not bother |
146 about allocating and deallocating memory to variables. Python provides extensibility |
503 about allocating and deallocating memory to variables. Python provides extensibility |
147 by providing modules which can be easily imported similar to headers in C and |
504 by providing modules which can be easily imported similar to headers in C and |
148 packages in Java. Python is object oriented and hence provides all the object oriented |
505 packages in Java. Python is object oriented and hence provides all the object oriented |
149 characteristics such as inheritance, encapsulation and polymorphism.</p></li> |
506 characteristics such as inheritance, encapsulation and polymorphism. |
150 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_13"></a>Python offers a highly powerful interactive programming interface in the form |
507 </p> |
|
508 </li> |
|
509 <li class="listitem" style="list-style-type: *"> |
|
510 <p id="ch2intro_13"> |
|
511 Python offers a highly powerful interactive programming interface in the form |
151 of the 'Interactive Interpreter' which will be discussed in more detail in the |
512 of the 'Interactive Interpreter' which will be discussed in more detail in the |
152 following sections.</p></li> |
513 following sections. |
153 <li class="listitem" style="list-style-type: *"> |
514 </p> |
154 <p><a name="ch2intro_14"></a>Python provides a rich standard library and an extensive set of modules. The |
515 </li> |
|
516 <li class="listitem" style="list-style-type: *"> |
|
517 <p id="ch2intro_14"> |
|
518 Python provides a rich standard library and an extensive set of modules. The |
155 power of Python modules can be seen in this slightly exaggerated cartoon |
519 power of Python modules can be seen in this slightly exaggerated cartoon |
156 </p> |
520 </p> |
157 <div class="reference"> |
521 <div class="reference"> |
158 <div class="titlepage"><hr></div>http://xkcd.com/353/</div> |
522 <div class="titlepage"> |
159 </li> |
523 <hr /> |
160 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_15"></a>Python interfaces well with most other programming languages such as C, C++ |
524 </div> |
161 and FORTRAN.</p></li> |
525 http://xkcd.com/353/ |
162 </ul></div> |
526 </div> |
163 <p><a name="ch2intro_16"></a>Although, Python has one setback. Python is not fast as some of the compiled |
527 </li> |
|
528 <li class="listitem" style="list-style-type: *"> |
|
529 <p id="ch2intro_15"> |
|
530 Python interfaces well with most other programming languages such as C, C++ |
|
531 and FORTRAN. |
|
532 </p> |
|
533 </li> |
|
534 </ul> |
|
535 </div> |
|
536 <p id="ch2intro_16"> |
|
537 Although, Python has one setback. Python is not fast as some of the compiled |
164 languages like C or C++. Yet, the amount of flexibility and power more than make |
538 languages like C or C++. Yet, the amount of flexibility and power more than make |
165 up for this setback.</p> |
539 up for this setback. |
166 </div> |
540 </p> |
167 <div class="section" title="2. The Python Interpreter"> |
541 </div> |
168 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
542 <div class="section" title="2.The Python Interpreter"> |
169 <a name="id2631374"></a>2. The Python Interpreter</h2></div></div></div> |
543 <div class="titlepage"> |
170 <div class="section" title="2.1. The Interactive Interpreter"> |
544 <div> |
171 <div class="titlepage"><div><div><h3 class="title"> |
545 <div> |
172 <a name="id2631383"></a>2.1. The Interactive Interpreter</h3></div></div></div> |
546 <h2 class="title" style="clear: both"> |
173 <p><a name="ch2intro_17"></a>Typing <span class="emphasis"><em>python</em></span> at the shell prompt on any standard Unix/Gnu-Linux system and |
547 <a name="id2860477"> |
|
548 </a> |
|
549 2.The Python Interpreter |
|
550 </h2> |
|
551 </div> |
|
552 </div> |
|
553 </div> |
|
554 <div class="section" title="2.1.The Interactive Interpreter"> |
|
555 <div class="titlepage"> |
|
556 <div> |
|
557 <div> |
|
558 <h3 class="title"> |
|
559 <a name="id2860486"> |
|
560 </a> |
|
561 2.1.The Interactive Interpreter |
|
562 </h3> |
|
563 </div> |
|
564 </div> |
|
565 </div> |
|
566 <p id="ch2intro_17"> |
|
567 Typing |
|
568 <span class="emphasis"> |
|
569 <em> |
|
570 python |
|
571 </em> |
|
572 </span> |
|
573 at the shell prompt on any standard Unix/Gnu-Linux system and |
174 hitting the enter key fires up the Python 'Interactive Interpreter'. The Python |
574 hitting the enter key fires up the Python 'Interactive Interpreter'. The Python |
175 interpreter is one of the most integral features of Python. The prompt obtained |
575 interpreter is one of the most integral features of Python. The prompt obtained |
176 when the interactive interpreter is similar to what is shown below. The exact |
576 when the interactive interpreter is similar to what is shown below. The exact |
177 appearance might differ based on the version of Python being used. The <code class="literal">>>></code> |
577 appearance might differ based on the version of Python being used. The |
178 thing shown is the python prompt. When something is typed at the prompt and the |
578 <code class="literal"> |
|
579 >>> |
|
580 </code> |
|
581 thing shown is the python prompt. When something is typed at the prompt and the |
179 enter key is hit, the python interpreter interprets the command entered and |
582 enter key is hit, the python interpreter interprets the command entered and |
180 performs the appropriate action. All the examples presented in this document are |
583 performs the appropriate action. All the examples presented in this document are |
181 to be tried hands on, on the interactive interpreter.</p> |
584 to be tried hands on, on the interactive interpreter. |
182 <pre class="programlisting">Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49) |
585 </p> |
|
586 <pre class="programlisting"> |
|
587 Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49) |
183 [GCC 4.3.2] on linux2 |
588 [GCC 4.3.2] on linux2 |
184 Type "help", "copyright", "credits" or "license" for more information. |
589 Type "help", "copyright", "credits" or "license" for more information. |
185 >>></pre> |
590 >>> |
186 <p><a name="ch2intro_18"></a>Lets try with an example, type <code class="literal">print 'Hello, World!'</code> at the prompt and hit |
591 </pre> |
187 the enter key.</p> |
592 <p id="ch2intro_18"> |
188 <pre class="programlisting">>>> print 'Hello, World!' |
593 Lets try with an example, type |
189 Hello, World!</pre> |
594 <code class="literal"> |
190 <p><a name="ch2intro_19"></a>This example was quite straight forward, and thus we have written our first |
595 print 'Hello, World!' |
|
596 </code> |
|
597 at the prompt and hit |
|
598 the enter key. |
|
599 </p> |
|
600 <pre class="programlisting"> |
|
601 >>> print 'Hello, World!' |
|
602 Hello, World! |
|
603 </pre> |
|
604 <p id="ch2intro_19"> |
|
605 This example was quite straight forward, and thus we have written our first |
191 line of Python code. Now let us try typing something arbitrary at the prompt. |
606 line of Python code. Now let us try typing something arbitrary at the prompt. |
192 For example:</p> |
607 For example: |
193 <pre class="programlisting">>>> arbit word |
608 </p> |
|
609 <pre class="programlisting"> |
|
610 >>> arbit word |
194 File "<stdin>", line 1 |
611 File "<stdin>", line 1 |
195 arbit word |
612 arbit word |
196 ^ |
613 ^ |
197 SyntaxError: invalid syntax |
614 SyntaxError: invalid syntax |
198 >>></pre> |
615 >>> |
199 <p><a name="ch2intro_1a"></a>The interpreter gave an error message saying that 'arbit word' was invalid |
616 </pre> |
|
617 <p id="ch2intro_1a"> |
|
618 The interpreter gave an error message saying that 'arbit word' was invalid |
200 syntax which is valid. The interpreter is an amazing tool when learning to |
619 syntax which is valid. The interpreter is an amazing tool when learning to |
201 program in Python. The interpreter provides a help function that provides the |
620 program in Python. The interpreter provides a help function that provides the |
202 necessary documentation regarding all Python syntax, constructs, modules and |
621 necessary documentation regarding all Python syntax, constructs, modules and |
203 objects. Typing <span class="emphasis"><em>help()</em></span> at the prompt gives the following output:</p> |
622 objects. Typing |
204 <pre class="programlisting">>>> help() |
623 <span class="emphasis"> |
|
624 <em> |
|
625 help() |
|
626 </em> |
|
627 </span> |
|
628 at the prompt gives the following output: |
|
629 </p> |
|
630 <pre class="programlisting"> |
|
631 >>> help() |
205 |
632 |
206 Welcome to Python 2.5! This is the online help utility. |
633 Welcome to Python 2.5! This is the online help utility. |
207 |
634 |
208 If this is your first time using Python, you should definitely check out |
635 If this is your first time using Python, you should definitely check out |
209 the tutorial on the Internet at http://www.python.org/doc/tut/. |
636 the tutorial on the Internet at http://www.python.org/doc/tut/. |
215 To get a list of available modules, keywords, or topics, type "modules", |
642 To get a list of available modules, keywords, or topics, type "modules", |
216 "keywords", or "topics". Each module also comes with a one-line summary |
643 "keywords", or "topics". Each module also comes with a one-line summary |
217 of what it does; to list the modules whose summaries contain a given word |
644 of what it does; to list the modules whose summaries contain a given word |
218 such as "spam", type "modules spam". |
645 such as "spam", type "modules spam". |
219 |
646 |
220 help></pre> |
647 help> |
221 <p><a name="ch2intro_1b"></a>As mentioned in the output, entering the name of any module, keyword or topic |
648 </pre> |
|
649 <p id="ch2intro_1b"> |
|
650 As mentioned in the output, entering the name of any module, keyword or topic |
222 will provide the documentation and help regarding the same through the online |
651 will provide the documentation and help regarding the same through the online |
223 help utility. Pressing <span class="emphasis"><em>Ctrl+d</em></span> exits the help prompt and returns to the |
652 help utility. Pressing |
224 python prompt.</p> |
653 <span class="emphasis"> |
225 <p><a name="ch2intro_1c"></a>Let us now try a few examples at the python interpreter.</p> |
654 <em> |
226 <p><a name="ch2intro_1d"></a>Eg 1:</p> |
655 Ctrl+d |
227 <pre class="programlisting">>>> print 'Hello, python!' |
656 </em> |
|
657 </span> |
|
658 exits the help prompt and returns to the |
|
659 python prompt. |
|
660 </p> |
|
661 <p id="ch2intro_1c"> |
|
662 Let us now try a few examples at the python interpreter. |
|
663 </p> |
|
664 <p id="ch2intro_1d"> |
|
665 Eg 1: |
|
666 </p> |
|
667 <pre class="programlisting"> |
|
668 >>> print 'Hello, python!' |
228 Hello, python! |
669 Hello, python! |
229 >>></pre> |
670 >>> |
230 <p><a name="ch2intro_1e"></a>Eg 2:</p> |
671 </pre> |
231 <pre class="programlisting">>>> print 4321*567890 |
672 <p id="ch2intro_1e"> |
|
673 Eg 2: |
|
674 </p> |
|
675 <pre class="programlisting"> |
|
676 >>> print 4321*567890 |
232 2453852690 |
677 2453852690 |
233 >>></pre> |
678 >>> |
234 <p><a name="ch2intro_1f"></a>Eg 3:</p> |
679 </pre> |
235 <pre class="programlisting">>>> 4321*567890 |
680 <p id="ch2intro_1f"> |
|
681 Eg 3: |
|
682 </p> |
|
683 <pre class="programlisting"> |
|
684 >>> 4321*567890 |
236 2453852690L |
685 2453852690L |
237 >>></pre> |
686 >>> |
238 <pre class="programlisting">Note: Notice the 'L' at the end of the output. The 'L' signifies that the |
687 </pre> |
|
688 <pre class="programlisting"> |
|
689 Note: Notice the 'L' at the end of the output. The 'L' signifies that the |
239 output of the operation is of type *long*. It was absent in the previous |
690 output of the operation is of type *long*. It was absent in the previous |
240 example because we used the print statement. This is because *print* formats |
691 example because we used the print statement. This is because *print* formats |
241 the output before displaying.</pre> |
692 the output before displaying. |
242 <p><a name="ch2intro_20"></a>Eg 4:</p> |
693 </pre> |
243 <pre class="programlisting">>>> big = 12345678901234567890 ** 3 |
694 <p id="ch2intro_20"> |
|
695 Eg 4: |
|
696 </p> |
|
697 <pre class="programlisting"> |
|
698 >>> big = 12345678901234567890 ** 3 |
244 >>> print big |
699 >>> print big |
245 1881676372353657772490265749424677022198701224860897069000 |
700 1881676372353657772490265749424677022198701224860897069000 |
246 >>></pre> |
701 >>> |
247 <pre class="programlisting">This example is to show that unlike in C or C++ there is no limit on the |
702 </pre> |
248 value of an integer.</pre> |
703 <pre class="programlisting"> |
249 <p><a name="ch2intro_21"></a>Try this on the interactive interpreter: |
704 This example is to show that unlike in C or C++ there is no limit on the |
250 <code class="literal">import this</code></p> |
705 value of an integer. |
251 <p><a name="ch2intro_22"></a><span class="emphasis"><em>Hint: The output gives an idea of Power of Python</em></span></p> |
706 </pre> |
252 </div> |
707 <p id="ch2intro_21"> |
253 <div class="section" title="2.2. ipython - An enhanced interactive Python interpreter"> |
708 Try this on the interactive interpreter: |
254 <div class="titlepage"><div><div><h3 class="title"> |
709 <code class="literal"> |
255 <a name="id2631556"></a>2.2. <span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter</h3></div></div></div> |
710 import this |
256 <p><a name="ch2intro_23"></a>The power and the importance of the interactive interpreter was the highlight |
711 </code> |
|
712 </p> |
|
713 <p id="ch2intro_22"> |
|
714 <span class="emphasis"> |
|
715 <em> |
|
716 Hint: The output gives an idea of Power of Python |
|
717 </em> |
|
718 </span> |
|
719 </p> |
|
720 </div> |
|
721 <div class="section" title="2.2.ipython - An enhanced interactive Python interpreter"> |
|
722 <div class="titlepage"> |
|
723 <div> |
|
724 <div> |
|
725 <h3 class="title"> |
|
726 <a name="id2860659"> |
|
727 </a> |
|
728 2.2. |
|
729 <span class="emphasis"> |
|
730 <em> |
|
731 ipython |
|
732 </em> |
|
733 </span> |
|
734 - An enhanced interactive Python interpreter |
|
735 </h3> |
|
736 </div> |
|
737 </div> |
|
738 </div> |
|
739 <p id="ch2intro_23"> |
|
740 The power and the importance of the interactive interpreter was the highlight |
257 of the previous section. This section provides insight into the enhanced |
741 of the previous section. This section provides insight into the enhanced |
258 interpreter with more advanced set of features called <span class="strong"><strong>ipython</strong></span>. Entering |
742 interpreter with more advanced set of features called |
259 <span class="emphasis"><em>ipython</em></span> at the shell prompt fires up the interactive interpreter.</p> |
743 <span class="strong"> |
260 <pre class="programlisting">$ ipython |
744 <strong> |
|
745 ipython |
|
746 </strong> |
|
747 </span> |
|
748 . Entering |
|
749 <span class="emphasis"> |
|
750 <em> |
|
751 ipython |
|
752 </em> |
|
753 </span> |
|
754 at the shell prompt fires up the interactive interpreter. |
|
755 </p> |
|
756 <pre class="programlisting"> |
|
757 $ ipython |
261 Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49) |
758 Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49) |
262 Type "copyright", "credits" or "license" for more information. |
759 Type "copyright", "credits" or "license" for more information. |
263 |
760 |
264 IPython 0.8.4 -- An enhanced Interactive Python. |
761 IPython 0.8.4 -- An enhanced Interactive Python. |
265 ? -> Introduction and overview of IPython's features. |
762 ? -> Introduction and overview of IPython's features. |
266 %quickref -> Quick reference. |
763 %quickref -> Quick reference. |
267 help -> Python's own help system. |
764 help -> Python's own help system. |
268 object? -> Details about 'object'. ?object also works, ?? prints more. |
765 object? -> Details about 'object'. ?object also works, ?? prints more. |
269 |
766 |
270 In [1]:</pre> |
767 In [1]: |
271 <p><a name="ch2intro_24"></a>This is the output obtained upon firing ipython. The exact appearance may |
768 </pre> |
|
769 <p id="ch2intro_24"> |
|
770 This is the output obtained upon firing ipython. The exact appearance may |
272 change based on the Python version installed. The following are some of the |
771 change based on the Python version installed. The following are some of the |
273 various features provided by <span class="strong"><strong>ipython</strong></span>:</p> |
772 various features provided by |
274 <p><a name="ch2intro_25"></a>Suggestions - ipython provides suggestions of the possible methods and |
773 <span class="strong"> |
275 operations available for the given python object.</p> |
774 <strong> |
276 <p><a name="ch2intro_26"></a>Eg 5:</p> |
775 ipython |
277 <pre class="programlisting">In [4]: a = 6 |
776 </strong> |
|
777 </span> |
|
778 : |
|
779 </p> |
|
780 <p id="ch2intro_25"> |
|
781 Suggestions - ipython provides suggestions of the possible methods and |
|
782 operations available for the given python object. |
|
783 </p> |
|
784 <p id="ch2intro_26"> |
|
785 Eg 5: |
|
786 </p> |
|
787 <pre class="programlisting"> |
|
788 In [4]: a = 6 |
278 |
789 |
279 In [5]: a. |
790 In [5]: a. |
280 a.__abs__ a.__divmod__ a.__index__ a.__neg__ a.__rand__ a.__rmod__ a.__rxor__ |
791 a.__abs__ a.__divmod__ a.__index__ a.__neg__ a.__rand__ a.__rmod__ a.__rxor__ |
281 a.__add__ a.__doc__ a.__init__ a.__new__ a.__rdiv__ a.__rmul__ a.__setattr__ |
792 a.__add__ a.__doc__ a.__init__ a.__new__ a.__rdiv__ a.__rmul__ a.__setattr__ |
282 a.__and__ a.__float__ a.__int__ a.__nonzero__ a.__rdivmod__ a.__ror__ a.__str__ |
793 a.__and__ a.__float__ a.__int__ a.__nonzero__ a.__rdivmod__ a.__ror__ a.__str__ |
283 a.__class__ a.__floordiv__ a.__invert__ a.__oct__ a.__reduce__ a.__rpow__ a.__sub__ |
794 a.__class__ a.__floordiv__ a.__invert__ a.__oct__ a.__reduce__ a.__rpow__ a.__sub__ |
284 a.__cmp__ a.__getattribute__ a.__long__ a.__or__ a.__reduce_ex__ a.__rrshift__ a.__truediv__ |
795 a.__cmp__ a.__getattribute__ a.__long__ a.__or__ a.__reduce_ex__ a.__rrshift__ a.__truediv__ |
285 a.__coerce__ a.__getnewargs__ a.__lshift__ a.__pos__ a.__repr__ a.__rshift__ a.__xor__ |
796 a.__coerce__ a.__getnewargs__ a.__lshift__ a.__pos__ a.__repr__ a.__rshift__ a.__xor__ |
286 a.__delattr__ a.__hash__ a.__mod__ a.__pow__ a.__rfloordiv__ a.__rsub__ |
797 a.__delattr__ a.__hash__ a.__mod__ a.__pow__ a.__rfloordiv__ a.__rsub__ |
287 a.__div__ a.__hex__ a.__mul__ a.__radd__ a.__rlshift__ a.__rtruediv__</pre> |
798 a.__div__ a.__hex__ a.__mul__ a.__radd__ a.__rlshift__ a.__rtruediv__ |
288 <p><a name="ch2intro_27"></a>In this example, we initialized 'a' (a variable - a concept that will be |
799 </pre> |
289 discussed in the subsequent sections.) to 6. In the next line when the <span class="emphasis"><em>tab</em></span> key |
800 <p id="ch2intro_27"> |
290 is pressed after typing '<span class="emphasis"><em>a.</em></span>' ipython displays the set of all possible methods |
801 In this example, we initialized 'a' (a variable - a concept that will be |
|
802 discussed in the subsequent sections.) to 6. In the next line when the |
|
803 <span class="emphasis"> |
|
804 <em> |
|
805 tab |
|
806 </em> |
|
807 </span> |
|
808 key |
|
809 is pressed after typing ' |
|
810 <span class="emphasis"> |
|
811 <em> |
|
812 a. |
|
813 </em> |
|
814 </span> |
|
815 ' ipython displays the set of all possible methods |
291 that are applicable on the object 'a' (an integer in this context). Ipython |
816 that are applicable on the object 'a' (an integer in this context). Ipython |
292 provides many such datatype specific features which will be presented in the |
817 provides many such datatype specific features which will be presented in the |
293 further sections as and when the datatypes are introduced.</p> |
818 further sections as and when the datatypes are introduced. |
294 </div> |
819 </p> |
295 </div> |
820 </div> |
296 <div class="section" title="3. Editing and running a python file"> |
821 </div> |
297 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
822 <div class="section" title="3.Editing and running a python file"> |
298 <a name="id2631681"></a>3. Editing and running a python file</h2></div></div></div> |
823 <div class="titlepage"> |
299 <p><a name="ch2intro_28"></a>The previous sections focused on the use of the interpreter to run python code. |
824 <div> |
|
825 <div> |
|
826 <h2 class="title" style="clear: both"> |
|
827 <a name="id2860784"> |
|
828 </a> |
|
829 3.Editing and running a python file |
|
830 </h2> |
|
831 </div> |
|
832 </div> |
|
833 </div> |
|
834 <p id="ch2intro_28"> |
|
835 The previous sections focused on the use of the interpreter to run python code. |
300 While the interpeter is an excellent tool to test simple solutions and |
836 While the interpeter is an excellent tool to test simple solutions and |
301 experiment with small code snippets, its main disadvantage is that everything |
837 experiment with small code snippets, its main disadvantage is that everything |
302 written in the interpreter is lost once its quit. Most of the times a program is |
838 written in the interpreter is lost once its quit. Most of the times a program is |
303 used by people other than the author. So the programs have to be available in |
839 used by people other than the author. So the programs have to be available in |
304 some form suitable for distribution, and hence they are written in files. This |
840 some form suitable for distribution, and hence they are written in files. This |
305 section will focus on editing and running python files. Start by opening a text |
841 section will focus on editing and running python files. Start by opening a text |
306 editor ( it is recommended you choose one from the list at the top of this page ). |
842 editor ( it is recommended you choose one from the list at the top of this page ). |
307 In the editor type down python code and save the file with an extension <span class="strong"><strong>.py</strong></span> |
843 In the editor type down python code and save the file with an extension |
308 (python files have an extension of .py). Once done with the editing, save the |
844 <span class="strong"> |
309 file and exit the editor.</p> |
845 <strong> |
310 <p><a name="ch2intro_29"></a>Let us look at a simple example of calculating the gcd of 2 numbers using Python:</p> |
846 .py |
311 <p><a name="ch2intro_2a"></a><span class="strong"><strong>Creating the first python script(file)</strong></span></p> |
847 </strong> |
312 <pre class="programlisting">$ emacs gcd.py |
848 </span> |
|
849 (python files have an extension of .py). Once done with the editing, save the |
|
850 file and exit the editor. |
|
851 </p> |
|
852 <p id="ch2intro_29"> |
|
853 Let us look at a simple example of calculating the gcd of 2 numbers using Python: |
|
854 </p> |
|
855 <p id="ch2intro_2a"> |
|
856 <span class="strong"> |
|
857 <strong> |
|
858 Creating the first python script(file) |
|
859 </strong> |
|
860 </span> |
|
861 </p> |
|
862 <pre class="programlisting"> |
|
863 $ emacs gcd.py |
313 def gcd(x,y): |
864 def gcd(x,y): |
314 if x % y == 0: |
865 if x % y == 0: |
315 return y |
866 return y |
316 return gcd(y, x%y) |
867 return gcd(y, x%y) |
317 |
868 |
318 print gcd(72, 92)</pre> |
869 print gcd(72, 92) |
319 <p><a name="ch2intro_2b"></a>To run the script, open the shell prompt, navigate to the directory that |
870 </pre> |
320 contains the python file and run <code class="literal">python <filename.py></code> at the prompt ( in this |
871 <p id="ch2intro_2b"> |
321 case filename is gcd.py )</p> |
872 To run the script, open the shell prompt, navigate to the directory that |
322 <p><a name="ch2intro_2c"></a><span class="strong"><strong>Running the python script</strong></span></p> |
873 contains the python file and run |
323 <pre class="programlisting">$ python gcd.py |
874 <code class="literal"> |
|
875 python <filename.py> |
|
876 </code> |
|
877 at the prompt ( in this |
|
878 case filename is gcd.py ) |
|
879 </p> |
|
880 <p id="ch2intro_2c"> |
|
881 <span class="strong"> |
|
882 <strong> |
|
883 Running the python script |
|
884 </strong> |
|
885 </span> |
|
886 </p> |
|
887 <pre class="programlisting"> |
|
888 $ python gcd.py |
324 4 |
889 4 |
325 $</pre> |
890 $ |
326 <p><a name="ch2intro_2d"></a>Another method to run a python script would be to include the line</p> |
891 </pre> |
327 <p><a name="ch2intro_2e"></a><code class="literal">#! /usr/bin/python</code></p> |
892 <p id="ch2intro_2d"> |
328 <p><a name="ch2intro_2f"></a>at the beginning of the python file and then make the file executable by</p> |
893 Another method to run a python script would be to include the line |
329 <p><a name="ch2intro_30"></a>$ chmod a+x <span class="emphasis"><em>filename.py</em></span></p> |
894 </p> |
330 <p><a name="ch2intro_31"></a>Once this is done, the script can be run as a standalone program as follows:</p> |
895 <p id="ch2intro_2e"> |
331 <p><a name="ch2intro_32"></a>$ ./<span class="emphasis"><em>filename.py</em></span></p> |
896 <code class="literal"> |
332 </div> |
897 #! /usr/bin/python |
333 <div class="section" title="4. Basic Datatypes and operators in Python"> |
898 </code> |
334 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
899 </p> |
335 <a name="id2631788"></a>4. Basic Datatypes and operators in Python</h2></div></div></div> |
900 <p id="ch2intro_2f"> |
336 <p><a name="ch2intro_33"></a>Python provides the following set of basic datatypes.</p> |
901 at the beginning of the python file and then make the file executable by |
337 <div class="itemizedlist"><ul class="itemizedlist" type="*"> |
902 </p> |
338 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_34"></a>Numbers: int, float, long, complex</p></li> |
903 <p id="ch2intro_30"> |
339 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_35"></a>Strings</p></li> |
904 $ chmod a+x |
340 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_36"></a>Boolean</p></li> |
905 <span class="emphasis"> |
341 </ul></div> |
906 <em> |
342 <div class="section" title="4.1. Numbers"> |
907 filename.py |
343 <div class="titlepage"><div><div><h3 class="title"> |
908 </em> |
344 <a name="id2631822"></a>4.1. Numbers</h3></div></div></div> |
909 </span> |
345 <p><a name="ch2intro_37"></a>Numbers were introduced in the examples presented in the interactive interpreter |
910 </p> |
|
911 <p id="ch2intro_31"> |
|
912 Once this is done, the script can be run as a standalone program as follows: |
|
913 </p> |
|
914 <p id="ch2intro_32"> |
|
915 $ ./ |
|
916 <span class="emphasis"> |
|
917 <em> |
|
918 filename.py |
|
919 </em> |
|
920 </span> |
|
921 </p> |
|
922 </div> |
|
923 <div class="section" title="4.Basic Datatypes and operators in Python"> |
|
924 <div class="titlepage"> |
|
925 <div> |
|
926 <div> |
|
927 <h2 class="title" style="clear: both"> |
|
928 <a name="id2860890"> |
|
929 </a> |
|
930 4.Basic Datatypes and operators in Python |
|
931 </h2> |
|
932 </div> |
|
933 </div> |
|
934 </div> |
|
935 <p id="ch2intro_33"> |
|
936 Python provides the following set of basic datatypes. |
|
937 </p> |
|
938 <div class="itemizedlist"> |
|
939 <ul class="itemizedlist" type="*"> |
|
940 <li class="listitem" style="list-style-type: *"> |
|
941 <p id="ch2intro_34"> |
|
942 Numbers: int, float, long, complex |
|
943 </p> |
|
944 </li> |
|
945 <li class="listitem" style="list-style-type: *"> |
|
946 <p id="ch2intro_35"> |
|
947 Strings |
|
948 </p> |
|
949 </li> |
|
950 <li class="listitem" style="list-style-type: *"> |
|
951 <p id="ch2intro_36"> |
|
952 Boolean |
|
953 </p> |
|
954 </li> |
|
955 </ul> |
|
956 </div> |
|
957 <div class="section" title="4.1.Numbers"> |
|
958 <div class="titlepage"> |
|
959 <div> |
|
960 <div> |
|
961 <h3 class="title"> |
|
962 <a name="id2860925"> |
|
963 </a> |
|
964 4.1.Numbers |
|
965 </h3> |
|
966 </div> |
|
967 </div> |
|
968 </div> |
|
969 <p id="ch2intro_37"> |
|
970 Numbers were introduced in the examples presented in the interactive interpreter |
346 section. Numbers include types as mentioned earlier viz., int (integers), float |
971 section. Numbers include types as mentioned earlier viz., int (integers), float |
347 (floating point numbers), long (large integers), complex (complex numbers with |
972 (floating point numbers), long (large integers), complex (complex numbers with |
348 real and imaginary parts). Python is not a strongly typed language, which means |
973 real and imaginary parts). Python is not a strongly typed language, which means |
349 the type of a variable need not mentioned during its initialization. Let us look |
974 the type of a variable need not mentioned during its initialization. Let us look |
350 at a few examples.</p> |
975 at a few examples. |
351 <p><a name="ch2intro_38"></a>Eg 6:</p> |
976 </p> |
352 <pre class="programlisting">>>> a = 1 #here a is an integer variable</pre> |
977 <p id="ch2intro_38"> |
353 <p><a name="ch2intro_39"></a>Eg 7:</p> |
978 Eg 6: |
354 <pre class="programlisting">>>> lng = 122333444455555666666777777788888888999999999 #here lng is a variable of type long |
979 </p> |
|
980 <pre class="programlisting"> |
|
981 >>> a = 1 #here a is an integer variable |
|
982 </pre> |
|
983 <p id="ch2intro_39"> |
|
984 Eg 7: |
|
985 </p> |
|
986 <pre class="programlisting"> |
|
987 >>> lng = 122333444455555666666777777788888888999999999 #here lng is a variable of type long |
355 >>> lng |
988 >>> lng |
356 122333444455555666666777777788888888999999999L #notice the trailing 'L' |
989 122333444455555666666777777788888888999999999L #notice the trailing 'L' |
357 >>> print lng |
990 >>> print lng |
358 122333444455555666666777777788888888999999999 #notice the absence of the trailing 'L' |
991 122333444455555666666777777788888888999999999 #notice the absence of the trailing 'L' |
359 >>> lng+1 |
992 >>> lng+1 |
360 122333444455555666666777777788888889000000000L</pre> |
993 122333444455555666666777777788888889000000000L |
361 <p><a name="ch2intro_3a"></a>Long numbers are the same as integers in almost all aspects. They can be used in |
994 </pre> |
|
995 <p id="ch2intro_3a"> |
|
996 Long numbers are the same as integers in almost all aspects. They can be used in |
362 operations just like integers and along with integers without any distinction. |
997 operations just like integers and along with integers without any distinction. |
363 The only distinction comes during type checking (which is not a healthy practice). |
998 The only distinction comes during type checking (which is not a healthy practice). |
364 Long numbers are tucked with a trailing 'L' just to signify that they are long. |
999 Long numbers are tucked with a trailing 'L' just to signify that they are long. |
365 Notice that in the example just lng at the prompt displays the value of the variable |
1000 Notice that in the example just lng at the prompt displays the value of the variable |
366 with the 'L' whereas <code class="literal">print lng</code> displays without the 'L'. This is because print |
1001 with the 'L' whereas |
|
1002 <code class="literal"> |
|
1003 print lng |
|
1004 </code> |
|
1005 displays without the 'L'. This is because print |
367 formats the output before printing. Also in the example, notice that adding an |
1006 formats the output before printing. Also in the example, notice that adding an |
368 integer to a long does not give any errors and the result is as expected. So for |
1007 integer to a long does not give any errors and the result is as expected. So for |
369 all practical purposes longs can be treated as ints.</p> |
1008 all practical purposes longs can be treated as ints. |
370 <p><a name="ch2intro_3b"></a>Eg 8:</p> |
1009 </p> |
371 <pre class="programlisting">>>> fl = 3.14159 #fl is a float variable |
1010 <p id="ch2intro_3b"> |
|
1011 Eg 8: |
|
1012 </p> |
|
1013 <pre class="programlisting"> |
|
1014 >>> fl = 3.14159 #fl is a float variable |
372 >>> e = 1.234e-4 #e is also a float variable, specified in the exponential form |
1015 >>> e = 1.234e-4 #e is also a float variable, specified in the exponential form |
373 >>> a = 1 |
1016 >>> a = 1 |
374 >>> b = 2 |
1017 >>> b = 2 |
375 >>> a/b #integer division |
1018 >>> a/b #integer division |
376 0 |
1019 0 |
377 >>> a/fl #floating point division |
1020 >>> a/fl #floating point division |
378 0.31831015504887655 |
1021 0.31831015504887655 |
379 >>> e/fl |
1022 >>> e/fl |
380 3.9279473133031364e-05</pre> |
1023 3.9279473133031364e-05 |
381 <p><a name="ch2intro_3c"></a>Floating point numbers, simply called floats are real numbers with a decimal point. |
1024 </pre> |
|
1025 <p id="ch2intro_3c"> |
|
1026 Floating point numbers, simply called floats are real numbers with a decimal point. |
382 The example above shows the initialization of a float variable. Shown also in this |
1027 The example above shows the initialization of a float variable. Shown also in this |
383 example is the difference between integer division and floating point division. |
1028 example is the difference between integer division and floating point division. |
384 'a' and 'b' here are integer variables and hence the division gives 0 as the quotient. |
1029 'a' and 'b' here are integer variables and hence the division gives 0 as the quotient. |
385 When either of the operands is a float, the operation is a floating point division, |
1030 When either of the operands is a float, the operation is a floating point division, |
386 and the result is also a float as illustrated.</p> |
1031 and the result is also a float as illustrated. |
387 <p><a name="ch2intro_3d"></a>Eg 9:</p> |
1032 </p> |
388 <pre class="programlisting">>>> cplx = 3 + 4j #cplx is a complex variable |
1033 <p id="ch2intro_3d"> |
|
1034 Eg 9: |
|
1035 </p> |
|
1036 <pre class="programlisting"> |
|
1037 >>> cplx = 3 + 4j #cplx is a complex variable |
389 >>> cplx |
1038 >>> cplx |
390 (3+4j) |
1039 (3+4j) |
391 >>> print cplx.real #prints the real part of the complex number |
1040 >>> print cplx.real #prints the real part of the complex number |
392 3.0 |
1041 3.0 |
393 >>> print cplx.imag #prints the imaginary part of the complex number |
1042 >>> print cplx.imag #prints the imaginary part of the complex number |
394 4.0 |
1043 4.0 |
395 >>> print cplx*fl #multiplies the real and imag parts of the complex number with the multiplier |
1044 >>> print cplx*fl #multiplies the real and imag parts of the complex number with the multiplier |
396 (9.42477+12.56636j) |
1045 (9.42477+12.56636j) |
397 >>> abs(cplx) #returns the absolute value of the complex number |
1046 >>> abs(cplx) #returns the absolute value of the complex number |
398 5.0</pre> |
1047 5.0 |
399 <p><a name="ch2intro_3e"></a>Python provides a datatype for complex numbers. Complex numbers are initialized |
1048 </pre> |
400 as shown in the example above. The <span class="emphasis"><em>real</em></span> and <span class="emphasis"><em>imag</em></span> operators return the real and |
1049 <p id="ch2intro_3e"> |
401 imaginary parts of the complex number as shown. The <span class="emphasis"><em>abs()</em></span> returns the absolute |
1050 Python provides a datatype for complex numbers. Complex numbers are initialized |
402 value of the complex number.</p> |
1051 as shown in the example above. The |
403 </div> |
1052 <span class="emphasis"> |
404 <div class="section" title="4.2. Variables"> |
1053 <em> |
405 <div class="titlepage"><div><div><h3 class="title"> |
1054 real |
406 <a name="id2631952"></a>4.2. Variables</h3></div></div></div> |
1055 </em> |
407 <p><a name="ch2intro_3f"></a>Variables are just names that represent a value. Variables have already been |
1056 </span> |
|
1057 and |
|
1058 <span class="emphasis"> |
|
1059 <em> |
|
1060 imag |
|
1061 </em> |
|
1062 </span> |
|
1063 operators return the real and |
|
1064 imaginary parts of the complex number as shown. The |
|
1065 <span class="emphasis"> |
|
1066 <em> |
|
1067 abs() |
|
1068 </em> |
|
1069 </span> |
|
1070 returns the absolute |
|
1071 value of the complex number. |
|
1072 </p> |
|
1073 </div> |
|
1074 <div class="section" title="4.2.Variables"> |
|
1075 <div class="titlepage"> |
|
1076 <div> |
|
1077 <div> |
|
1078 <h3 class="title"> |
|
1079 <a name="id2861055"> |
|
1080 </a> |
|
1081 4.2.Variables |
|
1082 </h3> |
|
1083 </div> |
|
1084 </div> |
|
1085 </div> |
|
1086 <p id="ch2intro_3f"> |
|
1087 Variables are just names that represent a value. Variables have already been |
408 introduced in the various examples from the previous sections. Certain rules about |
1088 introduced in the various examples from the previous sections. Certain rules about |
409 using variables:</p> |
1089 using variables: |
410 <div class="itemizedlist"><ul class="itemizedlist" type="*"> |
1090 </p> |
411 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_40"></a>Variables have to be initialized or assigned a value before being used.</p></li> |
1091 <div class="itemizedlist"> |
412 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_41"></a>Variable names can consist of letters, digits and underscores(_).</p></li> |
1092 <ul class="itemizedlist" type="*"> |
413 <li class="listitem" style="list-style-type: *"><p><a name="ch2intro_42"></a>Variable names cannot begin with digits, but can contain digits in them.</p></li> |
1093 <li class="listitem" style="list-style-type: *"> |
414 </ul></div> |
1094 <p id="ch2intro_40"> |
415 <p><a name="ch2intro_43"></a>In reference to the previous section examples, 'a', 'b', 'lng', 'fl', 'e' and 'cplx' |
1095 Variables have to be initialized or assigned a value before being used. |
416 are all variables of various datatypes.</p> |
1096 </p> |
417 <pre class="programlisting">Note: Python is not a strongly typed language and hence an integer variable can at a |
1097 </li> |
418 later stage be used as a float variable as well.</pre> |
1098 <li class="listitem" style="list-style-type: *"> |
419 </div> |
1099 <p id="ch2intro_41"> |
420 <div class="section" title="4.3. Strings"> |
1100 Variable names can consist of letters, digits and underscores(_). |
421 <div class="titlepage"><div><div><h3 class="title"> |
1101 </p> |
422 <a name="id2632000"></a>4.3. Strings</h3></div></div></div> |
1102 </li> |
423 <p><a name="ch2intro_44"></a>Strings are one of the essential data structures of any programming language. |
1103 <li class="listitem" style="list-style-type: *"> |
424 The <code class="literal">print "Hello, World!"</code> program was introduced in the earlier section, and |
1104 <p id="ch2intro_42"> |
425 the <span class="emphasis"><em>"Hello, World!"</em></span> in the print statement is a string. A string is basically |
1105 Variable names cannot begin with digits, but can contain digits in them. |
426 a set of characters. Strings can be represented in various ways shown below:</p> |
1106 </p> |
427 <pre class="programlisting">s = 'this is a string' # a string variable can be represented using single quotes |
1107 </li> |
|
1108 </ul> |
|
1109 </div> |
|
1110 <p id="ch2intro_43"> |
|
1111 In reference to the previous section examples, 'a', 'b', 'lng', 'fl', 'e' and 'cplx' |
|
1112 are all variables of various datatypes. |
|
1113 </p> |
|
1114 <pre class="programlisting"> |
|
1115 Note: Python is not a strongly typed language and hence an integer variable can at a |
|
1116 later stage be used as a float variable as well. |
|
1117 </pre> |
|
1118 </div> |
|
1119 <div class="section" title="4.3.Strings"> |
|
1120 <div class="titlepage"> |
|
1121 <div> |
|
1122 <div> |
|
1123 <h3 class="title"> |
|
1124 <a name="id2861102"> |
|
1125 </a> |
|
1126 4.3.Strings |
|
1127 </h3> |
|
1128 </div> |
|
1129 </div> |
|
1130 </div> |
|
1131 <p id="ch2intro_44"> |
|
1132 Strings are one of the essential data structures of any programming language. |
|
1133 The |
|
1134 <code class="literal"> |
|
1135 print "Hello, World!" |
|
1136 </code> |
|
1137 program was introduced in the earlier section, and |
|
1138 the |
|
1139 <span class="emphasis"> |
|
1140 <em> |
|
1141 "Hello, World!" |
|
1142 </em> |
|
1143 </span> |
|
1144 in the print statement is a string. A string is basically |
|
1145 a set of characters. Strings can be represented in various ways shown below: |
|
1146 </p> |
|
1147 <pre class="programlisting"> |
|
1148 s = 'this is a string' # a string variable can be represented using single quotes |
428 s = 'This one has "quotes" inside!' # The string can have quotes inside it as shown |
1149 s = 'This one has "quotes" inside!' # The string can have quotes inside it as shown |
429 s = "I have 'single-quotes' inside!" |
1150 s = "I have 'single-quotes' inside!" |
430 l = "A string spanning many lines\ |
1151 l = "A string spanning many lines |
431 one more line\ |
1152 one more line |
432 yet another" # a string can span more than a single line. |
1153 yet another" # a string can span more than a single line. |
433 t = """A triple quoted string does # another way of representing multiline strings. |
1154 t = """A triple quoted string does # another way of representing multiline strings. |
434 not need to be escaped at the end and |
1155 not need to be escaped at the end and |
435 "can have nested quotes" etc."""</pre> |
1156 "can have nested quotes" etc.""" |
436 <p><a name="ch2intro_45"></a>Try the following on the interpreter: |
1157 </pre> |
437 <code class="literal">s = 'this is a string with 'quotes' of similar kind'</code></p> |
1158 <p id="ch2intro_45"> |
438 <p><a name="ch2intro_46"></a><span class="strong"><strong>Exercise: How to use single quotes within single quotes in a string as shown |
1159 Try the following on the interpreter: |
439 in the above example without getting an error?</strong></span></p> |
1160 <code class="literal"> |
440 <div class="section" title="4.3.1. String operations"> |
1161 s = 'this is a string with 'quotes' of similar kind' |
441 <div class="titlepage"><div><div><h4 class="title"> |
1162 </code> |
442 <a name="id2632051"></a>4.3.1. String operations</h4></div></div></div> |
1163 </p> |
443 <p><a name="ch2intro_47"></a>A few basic string operations are presented here.</p> |
1164 <p id="ch2intro_46"> |
444 <p><a name="ch2intro_48"></a><span class="strong"><strong>String concatenation</strong></span> |
1165 <span class="strong"> |
445 String concatenation is done by simple addition of two strings.</p> |
1166 <strong> |
446 <pre class="programlisting">>>> x = 'Hello' |
1167 Exercise: How to use single quotes within single quotes in a string as shown |
|
1168 in the above example without getting an error? |
|
1169 </strong> |
|
1170 </span> |
|
1171 </p> |
|
1172 <div class="section" title="4.3.1.String operations"> |
|
1173 <div class="titlepage"> |
|
1174 <div> |
|
1175 <div> |
|
1176 <h4 class="title"> |
|
1177 <a name="id2861154"> |
|
1178 </a> |
|
1179 4.3.1.String operations |
|
1180 </h4> |
|
1181 </div> |
|
1182 </div> |
|
1183 </div> |
|
1184 <p id="ch2intro_47"> |
|
1185 A few basic string operations are presented here. |
|
1186 </p> |
|
1187 <p id="ch2intro_48"> |
|
1188 <span class="strong"> |
|
1189 <strong> |
|
1190 String concatenation |
|
1191 </strong> |
|
1192 </span> |
|
1193 String concatenation is done by simple addition of two strings. |
|
1194 </p> |
|
1195 <pre class="programlisting"> |
|
1196 >>> x = 'Hello' |
447 >>> y = ' Python' |
1197 >>> y = ' Python' |
448 >>> print x+y |
1198 >>> print x+y |
449 Hello Python</pre> |
1199 Hello Python |
450 <p><a name="ch2intro_49"></a><span class="emphasis"><em>Try this yourself:</em></span></p> |
1200 </pre> |
451 <pre class="programlisting">>>> somenum = 13 |
1201 <p id="ch2intro_49"> |
452 >>> print x+somenum</pre> |
1202 <span class="emphasis"> |
453 <p><a name="ch2intro_4a"></a>The problem with the above example is that here a string variable and an integer |
1203 <em> |
|
1204 Try this yourself: |
|
1205 </em> |
|
1206 </span> |
|
1207 </p> |
|
1208 <pre class="programlisting"> |
|
1209 >>> somenum = 13 |
|
1210 >>> print x+somenum |
|
1211 </pre> |
|
1212 <p id="ch2intro_4a"> |
|
1213 The problem with the above example is that here a string variable and an integer |
454 variable are trying to be concantenated. To obtain the desired result from the |
1214 variable are trying to be concantenated. To obtain the desired result from the |
455 above example the str(), repr() and the `` can be used.</p> |
1215 above example the str(), repr() and the `` can be used. |
456 <p><a name="ch2intro_4b"></a><span class="strong"><strong>str()</strong></span> simply converts a value to a string in a reasonable form. |
1216 </p> |
457 <span class="strong"><strong>repr()</strong></span> creates a string that is a representation of the value.</p> |
1217 <p id="ch2intro_4b"> |
458 <p><a name="ch2intro_4c"></a>The difference can be seen in the example shown below:</p> |
1218 <span class="strong"> |
459 <pre class="programlisting">>>> str(1000000000000000000000000000000000000000000000000L) |
1219 <strong> |
|
1220 str() |
|
1221 </strong> |
|
1222 </span> |
|
1223 simply converts a value to a string in a reasonable form. |
|
1224 <span class="strong"> |
|
1225 <strong> |
|
1226 repr() |
|
1227 </strong> |
|
1228 </span> |
|
1229 creates a string that is a representation of the value. |
|
1230 </p> |
|
1231 <p id="ch2intro_4c"> |
|
1232 The difference can be seen in the example shown below: |
|
1233 </p> |
|
1234 <pre class="programlisting"> |
|
1235 >>> str(1000000000000000000000000000000000000000000000000L) |
460 '1000000000000000000000000000000000000000000000000' |
1236 '1000000000000000000000000000000000000000000000000' |
461 >>> repr(1000000000000000000000000000000000000000000000000L) |
1237 >>> repr(1000000000000000000000000000000000000000000000000L) |
462 '1000000000000000000000000000000000000000000000000L'</pre> |
1238 '1000000000000000000000000000000000000000000000000L' |
463 <p><a name="ch2intro_4d"></a>It can be observed that the 'L' in the long value shown was omitted by str(), |
1239 </pre> |
|
1240 <p id="ch2intro_4d"> |
|
1241 It can be observed that the 'L' in the long value shown was omitted by str(), |
464 whereas repr() converted that into a string too. An alternative way of using |
1242 whereas repr() converted that into a string too. An alternative way of using |
465 repr(value) is <code class="literal">`value`</code>.</p> |
1243 repr(value) is |
466 <p><a name="ch2intro_4e"></a>A few more examples:</p> |
1244 <code class="literal"> |
467 <pre class="programlisting">>>> x = "Let's go \nto Pycon" |
1245 `value` |
|
1246 </code> |
|
1247 . |
|
1248 </p> |
|
1249 <p id="ch2intro_4e"> |
|
1250 A few more examples: |
|
1251 </p> |
|
1252 <pre class="programlisting"> |
|
1253 >>> x = "Let's go nto Pycon" |
468 >>> print x |
1254 >>> print x |
469 Let's go |
1255 Let's go |
470 to Pycon</pre> |
1256 to Pycon |
471 <p><a name="ch2intro_4f"></a>In the above example, notice that the 'n'(newline) character is formatted and |
1257 </pre> |
|
1258 <p id="ch2intro_4f"> |
|
1259 In the above example, notice that the 'n'(newline) character is formatted and |
472 the string is printed on two lines. The strings discussed until now were normal |
1260 the string is printed on two lines. The strings discussed until now were normal |
473 strings. Other than these there are two other types of strings namely, raw strings |
1261 strings. Other than these there are two other types of strings namely, raw strings |
474 and unicode strings.</p> |
1262 and unicode strings. |
475 <p><a name="ch2intro_50"></a><span class="strong"><strong>Raw strings</strong></span> are strings which are unformatted, that is the backslashes() are |
1263 </p> |
|
1264 <p id="ch2intro_50"> |
|
1265 <span class="strong"> |
|
1266 <strong> |
|
1267 Raw strings |
|
1268 </strong> |
|
1269 </span> |
|
1270 are strings which are unformatted, that is the backslashes() are |
476 not parsed and are left as it is in the string. Raw strings are represented with |
1271 not parsed and are left as it is in the string. Raw strings are represented with |
477 an 'r' at the start of a string. |
1272 an 'r' at the start of a string. |
478 Let us look at an example</p> |
1273 Let us look at an example |
479 <pre class="programlisting">>>> x = r"Let's go \nto Pycon" |
1274 </p> |
|
1275 <pre class="programlisting"> |
|
1276 >>> x = r"Let's go nto Pycon" |
480 >>> print x |
1277 >>> print x |
481 Let's go \nto Pycon</pre> |
1278 Let's go nto Pycon |
482 <p><a name="ch2intro_51"></a>Note: The 'n' is not being parsed into a new line and is left as it is.</p> |
1279 </pre> |
483 <p><a name="ch2intro_52"></a><span class="emphasis"><em>Try this yourself:</em></span></p> |
1280 <p id="ch2intro_51"> |
484 <pre class="programlisting">>>> x = r"Let's go to Pycon\"</pre> |
1281 Note: The 'n' is not being parsed into a new line and is left as it is. |
485 <p><a name="ch2intro_53"></a><span class="strong"><strong>Unicode strings</strong></span> are strings where the characters are Unicode characters as |
1282 </p> |
|
1283 <p id="ch2intro_52"> |
|
1284 <span class="emphasis"> |
|
1285 <em> |
|
1286 Try this yourself: |
|
1287 </em> |
|
1288 </span> |
|
1289 </p> |
|
1290 <pre class="programlisting"> |
|
1291 >>> x = r"Let's go to Pycon " |
|
1292 </pre> |
|
1293 <p id="ch2intro_53"> |
|
1294 <span class="strong"> |
|
1295 <strong> |
|
1296 Unicode strings |
|
1297 </strong> |
|
1298 </span> |
|
1299 are strings where the characters are Unicode characters as |
486 opposed to ASCII characters. Unicode strings are represented with a 'u' at the |
1300 opposed to ASCII characters. Unicode strings are represented with a 'u' at the |
487 start of the string. |
1301 start of the string. |
488 Let us look at an example:</p> |
1302 Let us look at an example: |
489 <pre class="programlisting">>>> x = u"Let's go to Pycon!" |
1303 </p> |
|
1304 <pre class="programlisting"> |
|
1305 >>> x = u"Let's go to Pycon!" |
490 >>> print x |
1306 >>> print x |
491 Let's go to Pycon!</pre> |
1307 Let's go to Pycon! |
492 </div> |
1308 </pre> |
493 </div> |
1309 </div> |
494 <div class="section" title="4.4. Boolean"> |
1310 </div> |
495 <div class="titlepage"><div><div><h3 class="title"> |
1311 <div class="section" title="4.4.Boolean"> |
496 <a name="id2632194"></a>4.4. Boolean</h3></div></div></div> |
1312 <div class="titlepage"> |
497 <p><a name="ch2intro_54"></a>Python also provides special Boolean datatype. A boolean variable can assume a |
1313 <div> |
498 value of either <span class="emphasis"><em>True</em></span> or <span class="emphasis"><em>False</em></span> (Note the capitalizations).</p> |
1314 <div> |
499 <p><a name="ch2intro_55"></a>Let us look at examples:</p> |
1315 <h3 class="title"> |
500 <pre class="programlisting">>>> t = True |
1316 <a name="id2861297"> |
|
1317 </a> |
|
1318 4.4.Boolean |
|
1319 </h3> |
|
1320 </div> |
|
1321 </div> |
|
1322 </div> |
|
1323 <p id="ch2intro_54"> |
|
1324 Python also provides special Boolean datatype. A boolean variable can assume a |
|
1325 value of either |
|
1326 <span class="emphasis"> |
|
1327 <em> |
|
1328 True |
|
1329 </em> |
|
1330 </span> |
|
1331 or |
|
1332 <span class="emphasis"> |
|
1333 <em> |
|
1334 False |
|
1335 </em> |
|
1336 </span> |
|
1337 (Note the capitalizations). |
|
1338 </p> |
|
1339 <p id="ch2intro_55"> |
|
1340 Let us look at examples: |
|
1341 </p> |
|
1342 <pre class="programlisting"> |
|
1343 >>> t = True |
501 >>> f = not t |
1344 >>> f = not t |
502 >>> print f |
1345 >>> print f |
503 False |
1346 False |
504 >>> f or t |
1347 >>> f or t |
505 True |
1348 True |
506 >>> f and t |
1349 >>> f and t |
507 False</pre> |
1350 False |
508 </div> |
1351 </pre> |
509 </div> |
1352 </div> |
510 <div class="section" title="5. The while loop"> |
1353 </div> |
511 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
1354 <div class="section" title="5.The while loop"> |
512 <a name="id2632223"></a>5. The <span class="strong"><strong>while</strong></span> loop</h2></div></div></div> |
1355 <div class="titlepage"> |
513 <p><a name="ch2intro_56"></a>The Python <span class="strong"><strong>while</strong></span> loop is similar to the C/C++ while loop. The syntax is as |
1356 <div> |
514 follows:</p> |
1357 <div> |
515 <pre class="programlisting">statement 0 |
1358 <h2 class="title" style="clear: both"> |
|
1359 <a name="id2861325"> |
|
1360 </a> |
|
1361 5.The |
|
1362 <span class="strong"> |
|
1363 <strong> |
|
1364 while |
|
1365 </strong> |
|
1366 </span> |
|
1367 loop |
|
1368 </h2> |
|
1369 </div> |
|
1370 </div> |
|
1371 </div> |
|
1372 <p id="ch2intro_56"> |
|
1373 The Python |
|
1374 <span class="strong"> |
|
1375 <strong> |
|
1376 while |
|
1377 </strong> |
|
1378 </span> |
|
1379 loop is similar to the C/C++ while loop. The syntax is as |
|
1380 follows: |
|
1381 </p> |
|
1382 <pre class="programlisting"> |
|
1383 statement 0 |
516 while condition: |
1384 while condition: |
517 statement 1 #while block |
1385 statement 1 #while block |
518 statement 2 #while block |
1386 statement 2 #while block |
519 statement 3 #outside the while block.</pre> |
1387 statement 3 #outside the while block. |
520 <p><a name="ch2intro_57"></a>Let us look at an example:</p> |
1388 </pre> |
521 <pre class="programlisting">>>> x = 1 |
1389 <p id="ch2intro_57"> |
|
1390 Let us look at an example: |
|
1391 </p> |
|
1392 <pre class="programlisting"> |
|
1393 >>> x = 1 |
522 >>> while x <= 5: |
1394 >>> while x <= 5: |
523 ... print x |
1395 ... print x |
524 ... x += 1 |
1396 ... x += 1 |
525 ... |
1397 ... |
526 1 |
1398 1 |
527 2 |
1399 2 |
528 3 |
1400 3 |
529 4 |
1401 4 |
530 5</pre> |
1402 5 |
531 </div> |
1403 </pre> |
532 <div class="section" title="6. The if conditional"> |
1404 </div> |
533 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
1405 <div class="section" title="6.The if conditional"> |
534 <a name="id2632260"></a>6. The <span class="strong"><strong>if</strong></span> conditional</h2></div></div></div> |
1406 <div class="titlepage"> |
535 <p><a name="ch2intro_58"></a>The Python <span class="strong"><strong>if</strong></span> block provides the conditional execution of statements. |
1407 <div> |
|
1408 <div> |
|
1409 <h2 class="title" style="clear: both"> |
|
1410 <a name="id2861363"> |
|
1411 </a> |
|
1412 6.The |
|
1413 <span class="strong"> |
|
1414 <strong> |
|
1415 if |
|
1416 </strong> |
|
1417 </span> |
|
1418 conditional |
|
1419 </h2> |
|
1420 </div> |
|
1421 </div> |
|
1422 </div> |
|
1423 <p id="ch2intro_58"> |
|
1424 The Python |
|
1425 <span class="strong"> |
|
1426 <strong> |
|
1427 if |
|
1428 </strong> |
|
1429 </span> |
|
1430 block provides the conditional execution of statements. |
536 If the condition evaluates as true the block of statements defined under the if |
1431 If the condition evaluates as true the block of statements defined under the if |
537 block are executed.</p> |
1432 block are executed. |
538 <p><a name="ch2intro_59"></a>If the first block is not executed on account of the condition not being satisfied, |
1433 </p> |
539 the set of statements in the <span class="strong"><strong>else</strong></span> block are executed.</p> |
1434 <p id="ch2intro_59"> |
540 <p><a name="ch2intro_5a"></a>The <span class="strong"><strong>elif</strong></span> block provides the functionality of evaluation of multiple conditions |
1435 If the first block is not executed on account of the condition not being satisfied, |
541 as shown in the example.</p> |
1436 the set of statements in the |
542 <p><a name="ch2intro_5b"></a>The syntax is as follows:</p> |
1437 <span class="strong"> |
543 <pre class="programlisting">if condition : |
1438 <strong> |
|
1439 else |
|
1440 </strong> |
|
1441 </span> |
|
1442 block are executed. |
|
1443 </p> |
|
1444 <p id="ch2intro_5a"> |
|
1445 The |
|
1446 <span class="strong"> |
|
1447 <strong> |
|
1448 elif |
|
1449 </strong> |
|
1450 </span> |
|
1451 block provides the functionality of evaluation of multiple conditions |
|
1452 as shown in the example. |
|
1453 </p> |
|
1454 <p id="ch2intro_5b"> |
|
1455 The syntax is as follows: |
|
1456 </p> |
|
1457 <pre class="programlisting"> |
|
1458 if condition : |
544 statement_1 |
1459 statement_1 |
545 statement_2 |
1460 statement_2 |
546 |
1461 |
547 elif condition: |
1462 elif condition: |
548 statement_3 |
1463 statement_3 |
549 statement_4 |
1464 statement_4 |
550 else: |
1465 else: |
551 statement_5 |
1466 statement_5 |
552 statement_6</pre> |
1467 statement_6 |
553 <p><a name="ch2intro_5c"></a>Let us look at an example:</p> |
1468 </pre> |
554 <pre class="programlisting">>>> n = raw_input("Input a number:") |
1469 <p id="ch2intro_5c"> |
|
1470 Let us look at an example: |
|
1471 </p> |
|
1472 <pre class="programlisting"> |
|
1473 >>> n = raw_input("Input a number:") |
555 >>> if n < 0: |
1474 >>> if n < 0: |
556 print n," is negative" |
1475 print n," is negative" |
557 elif n > 0: |
1476 elif n > 0: |
558 print n," is positive" |
1477 print n," is positive" |
559 else: |
1478 else: |
560 print n, " is 0"</pre> |
1479 print n, " is 0" |
561 </div> |
1480 </pre> |
562 <div class="section" title="7. raw_input()"> |
1481 </div> |
563 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
1482 <div class="section" title="7.raw_input()"> |
564 <a name="id2632330"></a>7. <span class="strong"><strong>raw_input()</strong></span> |
1483 <div class="titlepage"> |
565 </h2></div></div></div> |
1484 <div> |
566 <p><a name="ch2intro_5d"></a>In the previous example we saw the call to the raw_input() subroutine. |
1485 <div> |
567 The <span class="strong"><strong>raw_input()</strong></span> method is used to take user inputs through the console. |
1486 <h2 class="title" style="clear: both"> |
568 Unlike <span class="strong"><strong>input()</strong></span> which assumes the data entered by the user as a standard python |
1487 <a name="id2861432"> |
569 expression, <span class="strong"><strong>raw_input()</strong></span> treats all the input data as raw data and converts |
1488 </a> |
570 everything into a string. To illustrate this let us look at an example.</p> |
1489 7. |
571 <pre class="programlisting">>>> input("Enter a number thats a palindrome:") |
1490 <span class="strong"> |
|
1491 <strong> |
|
1492 raw_input() |
|
1493 </strong> |
|
1494 </span> |
|
1495 </h2> |
|
1496 </div> |
|
1497 </div> |
|
1498 </div> |
|
1499 <p id="ch2intro_5d"> |
|
1500 In the previous example we saw the call to the raw_input() subroutine. |
|
1501 The |
|
1502 <span class="strong"> |
|
1503 <strong> |
|
1504 raw_input() |
|
1505 </strong> |
|
1506 </span> |
|
1507 method is used to take user inputs through the console. |
|
1508 Unlike |
|
1509 <span class="strong"> |
|
1510 <strong> |
|
1511 input() |
|
1512 </strong> |
|
1513 </span> |
|
1514 which assumes the data entered by the user as a standard python |
|
1515 expression, |
|
1516 <span class="strong"> |
|
1517 <strong> |
|
1518 raw_input() |
|
1519 </strong> |
|
1520 </span> |
|
1521 treats all the input data as raw data and converts |
|
1522 everything into a string. To illustrate this let us look at an example. |
|
1523 </p> |
|
1524 <pre class="programlisting"> |
|
1525 >>> input("Enter a number thats a palindrome:") |
572 Enter a number thats a palindrome:121 |
1526 Enter a number thats a palindrome:121 |
573 121 |
1527 121 |
574 |
1528 |
575 >>> input("Enter your name:") |
1529 >>> input("Enter your name:") |
576 Enter your name:PythonFreak |
1530 Enter your name:PythonFreak |
577 Traceback (most recent call last): |
1531 Traceback (most recent call last): |
578 File "<stdin>", line 1, in <module> |
1532 File "<stdin>", line 1, in <module> |
579 File "<string>", line 1, in <module> |
1533 File "<string>", line 1, in <module> |
580 NameError: name 'PythonFreak' is not defined</pre> |
1534 NameError: name 'PythonFreak' is not defined |
581 <p><a name="ch2intro_5e"></a>As shown above the <span class="strong"><strong>input()</strong></span> assumes that the data entered is a valid Python |
1535 </pre> |
|
1536 <p id="ch2intro_5e"> |
|
1537 As shown above the |
|
1538 <span class="strong"> |
|
1539 <strong> |
|
1540 input() |
|
1541 </strong> |
|
1542 </span> |
|
1543 assumes that the data entered is a valid Python |
582 expression. In the first call it prompts for an integer input and when entered |
1544 expression. In the first call it prompts for an integer input and when entered |
583 it accepts the integer as an integer, whereas in the second call, when the string |
1545 it accepts the integer as an integer, whereas in the second call, when the string |
584 is entered without the quotes, <span class="strong"><strong>input()</strong></span> assumes that the entered data is a valid |
1546 is entered without the quotes, |
|
1547 <span class="strong"> |
|
1548 <strong> |
|
1549 input() |
|
1550 </strong> |
|
1551 </span> |
|
1552 assumes that the entered data is a valid |
585 Python expression and hence it raises and exception saying PythonFreak is not |
1553 Python expression and hence it raises and exception saying PythonFreak is not |
586 defined.</p> |
1554 defined. |
587 <pre class="programlisting">>>> input("Enter your name:") |
1555 </p> |
|
1556 <pre class="programlisting"> |
|
1557 >>> input("Enter your name:") |
588 Enter your name:'PythonFreak' |
1558 Enter your name:'PythonFreak' |
589 'PythonFreak' |
1559 'PythonFreak' |
590 >>></pre> |
1560 >>> |
591 <p><a name="ch2intro_5f"></a>Here the name is accepted because its entered as a string (within quotes). But |
1561 </pre> |
|
1562 <p id="ch2intro_5f"> |
|
1563 Here the name is accepted because its entered as a string (within quotes). But |
592 its unreasonable to go on using quotes each time a string is entered. Hence the |
1564 its unreasonable to go on using quotes each time a string is entered. Hence the |
593 alternative is to use <span class="strong"><strong>raw_input()</strong></span>.</p> |
1565 alternative is to use |
594 <p><a name="ch2intro_60"></a>Let us now look at how <span class="strong"><strong>raw_input()</strong></span> operates with an example.</p> |
1566 <span class="strong"> |
595 <pre class="programlisting">>>> raw_input("Enter your name:") |
1567 <strong> |
|
1568 raw_input() |
|
1569 </strong> |
|
1570 </span> |
|
1571 . |
|
1572 </p> |
|
1573 <p id="ch2intro_60"> |
|
1574 Let us now look at how |
|
1575 <span class="strong"> |
|
1576 <strong> |
|
1577 raw_input() |
|
1578 </strong> |
|
1579 </span> |
|
1580 operates with an example. |
|
1581 </p> |
|
1582 <pre class="programlisting"> |
|
1583 >>> raw_input("Enter your name:") |
596 Enter your name:PythonFreak |
1584 Enter your name:PythonFreak |
597 'PythonFreak'</pre> |
1585 'PythonFreak' |
598 <p><a name="ch2intro_61"></a>Observe that the <span class="strong"><strong>raw_input()</strong></span> is converting it into a string all by itself.</p> |
1586 </pre> |
599 <pre class="programlisting">>>> pal = raw_input("Enter a number thats a palindrome:") |
1587 <p id="ch2intro_61"> |
|
1588 Observe that the |
|
1589 <span class="strong"> |
|
1590 <strong> |
|
1591 raw_input() |
|
1592 </strong> |
|
1593 </span> |
|
1594 is converting it into a string all by itself. |
|
1595 </p> |
|
1596 <pre class="programlisting"> |
|
1597 >>> pal = raw_input("Enter a number thats a palindrome:") |
600 Enter a number thats a palindrome:121 |
1598 Enter a number thats a palindrome:121 |
601 '121'</pre> |
1599 '121' |
602 <p><a name="ch2intro_62"></a>Observe that <span class="strong"><strong>raw_input()</strong></span> is converting the integer 121 also to a string as |
1600 </pre> |
603 '121'. Let us look at another example:</p> |
1601 <p id="ch2intro_62"> |
604 <pre class="programlisting">>>> pal = raw_input("Enter a number thats a palindrome:") |
1602 Observe that |
|
1603 <span class="strong"> |
|
1604 <strong> |
|
1605 raw_input() |
|
1606 </strong> |
|
1607 </span> |
|
1608 is converting the integer 121 also to a string as |
|
1609 '121'. Let us look at another example: |
|
1610 </p> |
|
1611 <pre class="programlisting"> |
|
1612 >>> pal = raw_input("Enter a number thats a palindrome:") |
605 Enter a number thats a palindrome:121 |
1613 Enter a number thats a palindrome:121 |
606 >>> pal + 2 |
1614 >>> pal + 2 |
607 Traceback (most recent call last): |
1615 Traceback (most recent call last): |
608 File "<stdin>", line 1, in <module> |
1616 File "<stdin>", line 1, in <module> |
609 TypeError: cannot concatenate 'str' and 'int' objects |
1617 TypeError: cannot concatenate 'str' and 'int' objects |
610 >>> pal |
1618 >>> pal |
611 '121'</pre> |
1619 '121' |
612 <p><a name="ch2intro_63"></a>Observe here that the variable <span class="emphasis"><em>pal</em></span> is a string and hence integer operations |
1620 </pre> |
613 cannot be performed on it. Hence the exception is raised.</p> |
1621 <p id="ch2intro_63"> |
614 </div> |
1622 Observe here that the variable |
615 <div class="section" title="8. int() method"> |
1623 <span class="emphasis"> |
616 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
1624 <em> |
617 <a name="id2632484"></a>8. <span class="strong"><strong>int()</strong></span> method</h2></div></div></div> |
1625 pal |
618 <p><a name="ch2intro_64"></a>Generally for computing purposes, the data used is not strings or raw data but |
1626 </em> |
|
1627 </span> |
|
1628 is a string and hence integer operations |
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1629 cannot be performed on it. Hence the exception is raised. |
|
1630 </p> |
|
1631 </div> |
|
1632 <div class="section" title="8.int() method"> |
|
1633 <div class="titlepage"> |
|
1634 <div> |
|
1635 <div> |
|
1636 <h2 class="title" style="clear: both"> |
|
1637 <a name="id2861586"> |
|
1638 </a> |
|
1639 8. |
|
1640 <span class="strong"> |
|
1641 <strong> |
|
1642 int() |
|
1643 </strong> |
|
1644 </span> |
|
1645 method |
|
1646 </h2> |
|
1647 </div> |
|
1648 </div> |
|
1649 </div> |
|
1650 <p id="ch2intro_64"> |
|
1651 Generally for computing purposes, the data used is not strings or raw data but |
619 on integers, floats and similar mathematical data structures. The data obtained |
1652 on integers, floats and similar mathematical data structures. The data obtained |
620 from <span class="strong"><strong>raw_input()</strong></span> is raw data in the form of strings. In order to obtain integers |
1653 from |
621 from strings we use the method <span class="strong"><strong>int()</strong></span>.</p> |
1654 <span class="strong"> |
622 <p><a name="ch2intro_65"></a>Let us look at an example.</p> |
1655 <strong> |
623 <pre class="programlisting">>>> intpal = int(pal) |
1656 raw_input() |
|
1657 </strong> |
|
1658 </span> |
|
1659 is raw data in the form of strings. In order to obtain integers |
|
1660 from strings we use the method |
|
1661 <span class="strong"> |
|
1662 <strong> |
|
1663 int() |
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1664 </strong> |
|
1665 </span> |
|
1666 . |
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1667 </p> |
|
1668 <p id="ch2intro_65"> |
|
1669 Let us look at an example. |
|
1670 </p> |
|
1671 <pre class="programlisting"> |
|
1672 >>> intpal = int(pal) |
624 >>> intpal |
1673 >>> intpal |
625 121</pre> |
1674 121 |
626 <p><a name="ch2intro_66"></a>In the previous example it was observed that <span class="emphasis"><em>pal</em></span> was a string variable. Here |
1675 </pre> |
627 using the <span class="strong"><strong>int()</strong></span> method the string <span class="emphasis"><em>pal</em></span> was converted to an integer variable.</p> |
1676 <p id="ch2intro_66"> |
628 <p><a name="ch2intro_67"></a><span class="emphasis"><em>Try This Yourself:</em></span></p> |
1677 In the previous example it was observed that |
629 <pre class="programlisting">>>> stringvar = raw_input("Enter a name:") |
1678 <span class="emphasis"> |
|
1679 <em> |
|
1680 pal |
|
1681 </em> |
|
1682 </span> |
|
1683 was a string variable. Here |
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1684 using the |
|
1685 <span class="strong"> |
|
1686 <strong> |
|
1687 int() |
|
1688 </strong> |
|
1689 </span> |
|
1690 method the string |
|
1691 <span class="emphasis"> |
|
1692 <em> |
|
1693 pal |
|
1694 </em> |
|
1695 </span> |
|
1696 was converted to an integer variable. |
|
1697 </p> |
|
1698 <p id="ch2intro_67"> |
|
1699 <span class="emphasis"> |
|
1700 <em> |
|
1701 Try This Yourself: |
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1702 </em> |
|
1703 </span> |
|
1704 </p> |
|
1705 <pre class="programlisting"> |
|
1706 >>> stringvar = raw_input("Enter a name:") |
630 Enter a name:Guido Van Rossum |
1707 Enter a name:Guido Van Rossum |
631 >>> stringvar |
1708 >>> stringvar |
632 'Guido Van Rossum' |
1709 'Guido Van Rossum' |
633 >>> numvar = int(stringvar)</pre> |
1710 >>> numvar = int(stringvar) |
634 </div> |
1711 </pre> |
635 </div> |
1712 </div> |
636 </div></body> |
1713 </div> |
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1714 </div> |
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1715 </body> |
637 </html> |
1716 </html> |