Python – Loops

Most of the languages provides a way which makes it possible to carry out a sequence of statements repeatedly. The code within the loop, i.e. the code carried out repeatedly is called the body of the loop. 

Python supplies two different kinds of loops: the while loop and for loop. 

For

A simple for construct would like this,

>>> fruits = ["apple","mango","grape"]

>>> for fruit in fruits:

...     print fruit

...

apple

mango

grape

That reads, for every element that we assign the variable fruit, in the list fruits  print out the variable fruit

Other example looks as,

>>> numbers = [1,10,20,30,40]

>>> sum = 0

>>> for number in numbers:

...     sum = sum + number

...     print sum

...

1

11

…..

Break - If we need to break out of the loop ,we can use

>>> for i in range(1,10):

...     if i ==5:

...        break

...     print i

...

1

2

3

4

While

The While loop tells to perform an Operation as long as the condition defined is met. An basic example would look like this,

>>> fruits =  ["apple","mango","banana","grape"," raspberry"]

>>> i = 0

>>> while i < len(fruits):

...     print fruits[i]

...     i = i+1

...

apple

mango

banana

grape

raspberry

Another Example using while and reading Input,

>>> while True:

...     ans  = raw_input("Start Typing...")

...     if ans == "Q":

...             break

...     print "Enter Text was", ans

...

Start Typing...this is While Loop Q

Enter Text was this is While Loop Q

Nested Loops

Both for and while loops allow using Nested loops. Below is an Example,

>>> for x in range(1,11):

...     for y in range(11,1):

...             if x ==y:

...                     break

...             print x,y