.. 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   :
   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 the ``break``, ``continue`` and ``pass`` keywords
and how to use them. 

.. #[[Anoop: for loop is a pre-requisite and has been already covered,
   so i think our emphasize can be on while loops]]

.. #[[Anoop: Instead of saying we will learn keywords pass, break and
   continue, I think it is better to tell them that we will learn more
   about loops]]

{{{ 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 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.) 

.. #[[Anoop: can you be more explicit/specific on do no modify say we
   can ask them to use range(2, 10, 2) and solve the problem]]

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!