1 ======== |
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2 Script |
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3 ======== |
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4 |
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5 {{{ show the welcome slide }}} |
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6 |
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7 Welcome this tutorial on loops in Python. |
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8 |
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9 {{{ show the outline slide }}} |
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10 |
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11 In this tutorial, we shall look at ``while`` and ``for`` loops. We |
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12 shall then look at the ``break``, ``continue`` and ``pass`` keywords |
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13 and how to use them. |
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14 |
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15 {{{ switch to the ipython terminal }}} |
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16 |
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17 We have an ``ipython`` terminal, that we shall use through out this |
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18 tutorial. |
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19 |
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20 We shall first begin with the ``while`` loop. The ``while`` loop is |
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21 used for repeated execution as long as a condition is ``True``. |
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22 |
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23 Let us print the squares of all the odd numbers less than 10, using |
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24 the ``while`` loop. |
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25 |
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26 :: |
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27 |
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28 i = 1 |
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29 |
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30 while i<10: |
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31 print i*i |
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32 i += 2 |
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33 |
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34 This loop prints the squares of the odd numbers below 10. |
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35 |
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36 The ``while`` loop, repeatedly checks if the condition is true and |
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37 executes the block of code within the loop, if it is. As with any |
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38 other block in Python, the code within the ``while`` block is indented |
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39 to the right by 4 spaces. |
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40 |
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41 E%% %% Pause the video here and write a ``while`` loop to print the |
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42 squares of all the even numbers below 10. Then, return to the video. |
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43 |
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44 :: |
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45 |
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46 i = 2 |
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47 |
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48 while i<10: |
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49 print i*i |
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50 i += 2 |
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51 |
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52 Let us now solve the same problem of printing the squares of all odd |
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53 numbers less than 10, using the ``for`` loop. As we know, the ``for`` |
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54 loop iterates over a list or any other sequential data type. So, we |
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55 use the ``range`` function to get a list of odd numbers below 10, and |
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56 then iterate over it and print the required stuff. |
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57 |
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58 :: |
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59 |
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60 for n in range(1, 10, 2): |
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61 print n*n |
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62 |
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63 E%% %% Pause the video here and write a ``for`` loop to print the |
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64 squares of all the even numbers below 10. Then, return to the video. |
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65 |
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66 :: |
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67 |
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68 for n in range(2, 10, 2): |
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69 print n*n |
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70 |
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71 Let us now look at how to use the keywords, ``pass``, ``break`` and |
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72 ``continue``. |
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73 |
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74 As we already know, ``pass`` is just a syntactic filler. It is used |
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75 for the sake of completion of blocks, that do not have any code within |
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76 them. |
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77 |
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78 :: |
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79 |
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80 for n in range(2, 10, 2): |
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81 pass |
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82 |
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83 ``break`` is used to break out of the innermost loop. The ``while`` |
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84 loop to print the squares of all the odd numbers below 10, can be |
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85 modified using the ``break`` statement, as follows |
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86 :: |
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87 |
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88 i = 1 |
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89 |
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90 while True: |
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91 print i*i |
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92 i += 2 |
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93 if i<10: |
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94 break |
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95 |
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96 ``continue`` is used to skip execution of the rest of the loop on this |
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97 iteration and continue to the end of this iteration. |
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98 |
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99 Say, we wish to print the squares of all the odd numbers below 10, |
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100 which are not multiples of 3, we would modify the for loop as follows. |
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101 :: |
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102 |
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103 for n in range(1, 10, 2): |
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104 if n%3 == 0: |
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105 continue |
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106 print n*n |
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107 |
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108 |
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109 E%% %%Pause the video here and using the ``continue`` keyword modify |
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110 the ``for`` loop to print the squares of even numbers below 10, to |
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111 print the squares of only multiples of 4. (Do not modify the range |
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112 function call.) Then, resume the video. |
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113 :: |
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114 |
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115 for n in range(2, 10, 2): |
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116 if n%4: |
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117 continue |
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118 print n*n |
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119 |
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120 That brings us to the end of this tutorial. In this tutorial, we have |
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121 learnt about looping structures in Python and the use of the keywords |
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122 ``pass``, ``break`` and ``continue``. |
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123 |
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124 Thank You! |
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