diff -r 901b78003917 -r 01bb60f51398 loops.rst --- a/loops.rst Wed Oct 06 15:38:54 2010 +0530 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,124 +0,0 @@ -======== - Script -======== - -{{{ show the welcome slide }}} - -Welcome this tutorial on loops in Python. - -{{{ show the outline slide }}} - -In this tutorial, we shall look at ``while`` and ``for`` loops. We -shall then look at the ``break``, ``continue`` and ``pass`` keywords -and how to use them. - -{{{ switch to the ipython terminal }}} - -We have an ``ipython`` terminal, that we shall use through out this -tutorial. - -We shall first begin with the ``while`` loop. The ``while`` loop is -used for repeated execution as long as a condition is ``True``. - -Let us print the squares of all the odd numbers less than 10, using -the ``while`` loop. - -:: - - i = 1 - - while i<10: - print i*i - i += 2 - -This loop prints the squares of the odd numbers below 10. - -The ``while`` loop, repeatedly checks if the condition is true and -executes the block of code within the loop, if it is. As with any -other block in Python, the code within the ``while`` block is indented -to the right by 4 spaces. - -E%% %% Pause the video here and write a ``while`` loop to print the -squares of all the even numbers below 10. Then, return to the video. - -:: - - i = 2 - - while i<10: - print i*i - i += 2 - -Let us now solve the same problem of printing the squares of all odd -numbers less than 10, using the ``for`` loop. As we know, the ``for`` -loop iterates over a list or any other sequential data type. So, we -use the ``range`` function to get a list of odd numbers below 10, and -then iterate over it and print the required stuff. - -:: - - for n in range(1, 10, 2): - print n*n - -E%% %% Pause the video here and write a ``for`` loop to print the -squares of all the even numbers below 10. Then, return to the video. - -:: - - for n in range(2, 10, 2): - print n*n - -Let us now look at how to use the keywords, ``pass``, ``break`` and -``continue``. - -As we already know, ``pass`` is just a syntactic filler. It is used -for the sake of completion of blocks, that do not have any code within -them. - -:: - - for n in range(2, 10, 2): - pass - -``break`` is used to break out of the innermost loop. The ``while`` -loop to print the squares of all the odd numbers below 10, can be -modified using the ``break`` statement, as follows -:: - - i = 1 - - while True: - print i*i - i += 2 - if i<10: - break - -``continue`` is used to skip execution of the rest of the loop on this -iteration and continue to the end of this iteration. - -Say, we wish to print the squares of all the odd numbers below 10, -which are not multiples of 3, we would modify the for loop as follows. -:: - - for n in range(1, 10, 2): - if n%3 == 0: - continue - print n*n - - -E%% %%Pause the video here and using the ``continue`` keyword modify -the ``for`` loop to print the squares of even numbers below 10, to -print the squares of only multiples of 4. (Do not modify the range -function call.) Then, resume the video. -:: - - for n in range(2, 10, 2): - if n%4: - continue - print n*n - -That brings us to the end of this tutorial. In this tutorial, we have -learnt about looping structures in Python and the use of the keywords -``pass``, ``break`` and ``continue``. - -Thank You!