A while loop repeats code until the condition is met. Unlike for loops, the number of iterations in it may be unknown. A while loop always consists of a condition and a block of code.

A while loop ends if and only if the condition is true, in contrast to a for loop that always has a finite countable number of steps.

while loop

 

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Example

The while loop below defines the condition (x < 10) and repeats the instructions until that condition is true. Type this code:

#!/usr/bin/python

x = 3
while x < 10:
print(x)
x = x + 1

Executes the code below until the condition x < 10 is met. Unlike a for loop, the iterator i is increased in the loop.

Exercise

Try the exercise below:

1. Make a program that lists the countries in the set below using a while loop.

clist = ["Canada","USA","Mexico"]

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