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2012-11-29T06:17:00Z

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{| border=1
!Visual Cue
!Narration
|-
| Show Slide 1

Containing title, name of the production team along with the logo of MHRD
| Hello Friends and Welcome to the tutorial on 'loops' in Python.

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| Show Slide 2

Learning objectives
| At the end of this tutorial, you will be able to,

# use the <tt>for</tt> loop
# use the <tt>while</tt> loop
# Use <tt>break</tt>, <tt>continue</tt> and <tt>pass</tt> statements to play around with loops.

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| Show Slide 3

Pre-requisite slide
| Before beginning this tutorial,we would suggest you to complete the tutorial on "Getting started with for" and "Conditionals".

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| Switch to the ipython terminal

ipython
| Let us start our ipython interpreter.

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| i = 1

<nowiki>while i<10:</nowiki>
print i*i
i += 2
| We shall first begin with the <tt>while</tt> loop. The <tt>while</tt> loop is used for repeated execution as long as a condition is <tt>True</tt>.

Let us print the squares of all the odd numbers less than 10, using the <tt>while</tt> loop.

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| This loop prints the squares of the odd numbers below 10.

The <tt>while</tt> 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 <tt>while</tt> block is indented to the right by 4 spaces.

Pause the video here, try out the following exercise and resume the video.

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| Show Slide 4

Assignment 1
| '''Write a <tt>while</tt> loop to print the squares of all the even'''

numbers below 10.

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| Continue from paused state Switch to the terminal

i = 2

<nowiki>while i<10:</nowiki>
print i*i
i += 2
| Switch to the terminal for solution.

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| for n in range(1, 10, 2):
print n*n
| Let us now solve the same problem of printing the squares of all odd numbers less than 10, using the <tt>for</tt> loop. As we know, the <tt>for</tt> loop iterates over a list or any other sequential data type. So, we use the <tt>range</tt> function to get a list of odd numbers below 10, and then iterate over it and print the required stuff.

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| We can see that we got the same output as before. Note that the lines of code are less.

Pause the video here, try out the following exercise and resume the video.

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| Show Slide 5

Assignment 2
| '''Write a <tt>for</tt> loop to print the squares of all the even'''

numbers below 10.

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| Continue from paused state Switch to the terminal

for n in range(2, 10, 2):
print n*n
| Switch to the terminal for solution.

|-
| for n in range(2, 10, 2):
pass
| Let us now look at how to use the keywords, <tt>pass</tt>, <tt>break</tt> and <tt>continue</tt>.

As we already know, <tt>pass</tt> is just a syntactic filler. It is used for the sake of completion of blocks, that do not have any code within them.

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| i = 1

while True:
print i*i
i += 2
<nowiki>if i<10:</nowiki>
break
| <tt>break</tt> is used to break out of the innermost loop. The <tt>while</tt> loop to print the squares of all the odd numbers below 10, can be modified using the <tt>break</tt> statement, as follows

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| for n in range(1, 10, 2):
if n%3 == 0:
continue
print n*n
| <tt>continue</tt> 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 <tt>for</tt> loop as follows.

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|
| Pause the video here, try out the following exercise and resume the video.

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| Show Slide 6

Assignment 3
| Using the <tt>continue</tt> keyword modify the <tt>for</tt> loop, with the <tt>range(2, 10, 2)</tt>, to print the squares of even numbers below 10, which are multiples of 4. (Do not modify the range function call.)

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| Continue from paused state Switch to the terminal

for n in range(2, 10, 2):
if n%4:
continue
print n*n
| Switch to the terminal for solution.

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| Show Slide 7

Summary slide
| This brings us to the end of this tutorial. In this tutorial, we have learnt to,

# Iterate over a sequence using ``for'' and ``while'' loops. Inline literal start-string without end-string. Inline literal start-string without end-string.
# Break out of loops using ``break'' statement. Inline literal start-string without end-string.
# Skip iterations using ``continue'' statement. Inline literal start-string without end-string.
# Use the ``pass'' statement in a loop. Inline literal start-string without end-string.

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| Show Slide 8

Self assessment questions slide
| Here are some self assessment questions for you to solve

# Given <tt>range(1,4)</tt><nowiki>; Write a code to print only the number 1.</nowiki>
# Which statement do you use to skip iterations. - break - pass - continue

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| Show Slide 9

Solution of self assessment questions on slide
| And the answers,

# We can use the break statement in a for loop as,

'''::'''

'''for i in range(1, 4):'''

print i break

# In order to skip iterations,we make use of the <tt>continue</tt> statement.

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| Show Slide 10

Acknowledgment slide
| Hope you have enjoyed this tutorial and found it useful. Thank you!

|}

Python/C3/Loops/English - Revision history

Chandrika: Created page with '{| border=1 !Visual Cue !Narration |- | Show Slide 1 Containing title, name of the production team along with the logo of MHRD | Hello Friends and Welcome to the tutorial on '…'