22 In the previous tutorial we have looked at data types for dealing |
22 In the previous tutorial we have looked at data types for dealing |
23 with numbers. In this tutorial we shall look at strings. We shall |
23 with numbers. In this tutorial we shall look at strings. We shall |
24 look at how to do elementary string manipulation, and simple input |
24 look at how to do elementary string manipulation, and simple input |
25 and output operations. |
25 and output operations. |
26 |
26 |
27 In this tuotrial we shall use concepts of writing python scripts and basics of lists that have been covered in previous session |
27 In this tuotrial we shall use concepts of writing python scripts and |
|
28 basics of lists that have been covered in previous session |
28 |
29 |
29 Lets get started by opening ipython interpreter. |
30 Lets get started by opening ipython interpreter. |
30 We shall create some |
31 We shall create some |
31 a string by typing |
32 a string by typing |
32 |
33 |
33 a = open single quote 'This is a string' close single quote |
34 a = open single quote 'This is a string' close single quote |
34 print a |
35 print a |
35 a contains the string |
36 a contains the string |
36 we can check for datatype of a by using type(a) and shows it is 'str' |
37 we can check for datatype of a by using type(a) and shows it is 'str' |
37 |
38 |
38 consider the case when string contains single quote. |
39 consider the case when string contains single quote. |
39 for example I'll be back |
40 for example I'll be back |
40 to store these kind of strings, we use double quotes |
41 to store these kind of strings, we use double quotes |
50 quotes. |
51 quotes. |
51 |
52 |
52 so when you do |
53 so when you do |
53 c = '''Iam also a string''' |
54 c = '''Iam also a string''' |
54 print c |
55 print c |
55 and c is also string variable |
56 and c is also string variable |
56 and even |
57 and even |
57 d = """And one more.""" |
58 d = """And one more.""" |
58 print d |
59 print d |
59 d is also a string |
60 d is also a string |
60 |
61 |
61 These strings enclosed in triple quotes are special type of strings, called docstrings, and they shall |
62 These strings enclosed in triple quotes are special type of strings, called docstrings, and they shall |
62 be discussed in detail along with functions |
63 be discussed in detail along with functions |
63 |
64 |
64 We know elements in lists and arrays can be accessed with indices. |
65 We know elements in lists and arrays can be accessed with indices. |
152 Note that a, is now a string variable and not an integer. |
153 Note that a, is now a string variable and not an integer. |
153 type(a) |
154 type(a) |
154 raw_input takes input only as a string |
155 raw_input takes input only as a string |
155 |
156 |
156 we cannot do mathematical operations on it |
157 we cannot do mathematical operations on it |
157 but we can use type conversion similar to that shown in previous tutorial |
158 but we can use type conversion similar to that shown in previous tutorial |
158 |
159 |
159 b = int(a) |
160 b = int(a) |
160 a has now been converted to an integer and stored in b |
161 a has now been converted to an integer and stored in b |
161 type(b) gives int |
162 type(b) gives int |
162 b can be used here for mathematical operations. |
163 b can be used here for mathematical operations. |
163 |
164 |
164 For console output, we have been using print which is pretty straightforward. |
165 For console output, we have been using print which is pretty straightforward. |
165 |
166 |
166 We shall look at a subtle feature of the print statement. |
167 We shall look at a subtle feature of the print statement. |
167 |
168 |
179 We now run this file, from the ipython interpreter. |
180 We now run this file, from the ipython interpreter. |
180 %run hello2.py |
181 %run hello2.py |
181 |
182 |
182 |
183 |
183 Note the difference in the output. |
184 Note the difference in the output. |
184 The comma adds a space at the end of the line, instead |
185 The comma adds a space at the end of the line, instead |
185 of a new line character that is normally added. |
186 of a new line character that is normally added. |
186 |
187 |
187 Before we wind up, a couple of miscellaneous things. |
188 Before we wind up, a couple of miscellaneous things. |
188 As you may have already noticed, Python is a dynamically typed |
189 As you may have already noticed, Python is a dynamically typed |
189 language, that is you don't have to specify the type of a variable |
190 language, that is you don't have to specify the type of a variable |
190 when using a new one. You don't have to do anything special, to 'reuse' |
191 when using a new one. You don't have to do anything special, to 'reuse' |
191 a variable that was of int type as a float or string. |
192 a variable that was of int type as a float or string. |
192 |
193 |
193 a = 1 and here a is integer |
194 a = 1 and here a is integer |
194 lets store a float value in a by doing |
195 lets store a float value in a by doing |
195 a = 1.1 |
196 a = 1.1 |
196 and print a |
197 and print a |
197 now a is float |
198 now a is float |
198 a = "Now I am a string!" |
199 a = "Now I am a string!" |
199 |
200 |
200 Comments in Python start with a pound or hash sign. Anything after |
201 Comments in Python start with a pound or hash sign. Anything after |
201 a #, until the end of the line is considered a comment, except of |
202 a #, until the end of the line is considered a comment, except of |
202 course, if the hash is in a string. |
203 course, if the hash is in a string. |