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.. Objectives
.. ----------
.. By the end of this tutorial, you will be able to
.. 1. use the ``for`` loop
.. #. use the ``while`` loop
.. #. Use ``break``, ``continue`` and ``pass`` statements to play around
.. with loops.
.. Prerequisites
.. -------------
.. 1. getting started with ipython
.. #. getting started with for
.. #. conditionals
.. Author : Puneeth
Internal Reviewer : Anoop Jacob Thomas<anoop@fossee.in>
External Reviewer :
Langauge Reviewer : Bhanukiran
Checklist OK? : <put date stamp here, if OK> [2010-10-05]
Script
------
{{{ Show the slide containing title }}}
Hello Friends. Welcome to the 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 how to break out of them, or skip some iterations
in loops.
.. #[[Anoop: for loop is a pre-requisite and has been already covered,
so i think our emphasize can be on while loops]]
.. #[[punch: I think, we should have both of them. It gives a better
.. context and comparison.]
{{{ 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.
{{{ switch to next slide }}}
Following is an exercise that you must do.
%%1%% Write a ``while`` loop to print the squares of all the even
numbers below 10.
Please, pause the video here. Do the exercise and then continue.
{{{ switch to next slide after a seconds break}}}
::
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
Following is an exercise that you must do.
{{{ switch to next slide }}}
%%2%% Write a ``for`` loop to print the squares of all the even
numbers below 10.
Please, pause the video here. Do the exercise and then continue.
{{{ switch to next slide after a seconds break }}}
::
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.
.. #[[Anoop: should add slides for break, continue, pass]]
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
Following is an exercise that you must do.
{{{ switch to next slide }}}
%%3%%Using the ``continue`` keyword modify the ``for`` loop, with the
``range(2, 10, 2)``, to print the squares of even numbers below 10, to
print the squares of only multiples of 4.
Please, pause the video here. Do the exercise and then continue.
{{{ switch to next slide after a seconds break}}}
::
for n in range(2, 10, 2):
if n%4:
continue
print n*n
{{{ Show summary slide }}}
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``.
{{{ Show the "sponsored by FOSSEE" slide }}}
This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India
Hope you have enjoyed and found it useful.
Thank you!
|
