Python - While Loop

Python - While Loop

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A loop statement allows a program to execute statements(s) repeatedly under a given condition. This enables a programmer to write Python programs in fewer lines of code and enhance the code readability. In Python, there are two types of loop statements.

  • While loop
  • For loop

The While Loop

The While loop allows a set of statements to be executed repeatedly until a given condition is true. It can be viewed as a repeating if statement. A while loop is preferred over for loop whenever number of iteration is not known beforehand.

Syntax


while condition:
      statements

Flow Diagram:

Python While Loop

In below mentioned example, program uses while loop to sum all integers from 1 to 5.

Example

sum = 0
i = 1
while (i < 6):
    sum = sum + i
    i = i+1
print(sum)

Output

15

While loop with else statement

The else block can be used with while loop also. The else block is executed when condition check in while loop returns false.

Syntax


while condition:
      statements
else:
      statements

In below mentioned example, else code block is executed after exiting from while loop.

Example

i = 1
while (i < 6):
    print(i)
    i = i + 1
else:
    print('loop exhausted.')

Output

1
2
3
4
5
loop exhausted.

However, when program exits from while loop using break statements, it ignores the else block.

Example

i = 1
while (i < 6):
    print(i)
    i = i + 1
    if (i==4):
        break
else:
    print('loop exhausted.')

Output

1
2
3


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