Python Loops

Instead of writing the same code multiple times we use loop statement to execute group of statements several times. The loop statement will execute until satisfying the given condition.

Python provides the following types of loops,

Loop Type	Description
while loop	While loop repeats a statement or group of statements as long as a condition is true.
for loop	The for loop is a control flow statement, which allows code to be executed repeatedly.
nested loops	When we use a loop inside any other for loop or while loop then it is a nested loop.

while loop

While loop will execute a block of statement repeatedly until the given condition satisfies. The while loop consists of a condition block and it will keep on executing the statement until the condition becomes false.

Syntax:

while expression:
   statement

Example:

i = 0
while i < 5:
 print(i, "is less than 5")
 i = i + 1

Output:

0 is less than 5
1 is less than 5
2 is less than 5
3 is less than 5
4 is less than 5

else Statement

The else statement will execute when the while condition becomes false.

Example:

i = 0
while i < 5:
 print(i, "is less than 5")
 i = i + 1
else:
 print(i, "is greater than 5")

Output:

0 is less than 5
1 is less than 5
2 is less than 5
3 is less than 5
4 is less than 5
5 is greater than 5

break Statement

The break statement is used to stop the while loop even if the condition is true.

Example:

i = 0
while i < 10:
 print(i, "is less than 10")
 if i == 5:
  break
 i = i + 1

Output:

0 is less than 10
1 is less than 10
2 is less than 10
3 is less than 10
4 is less than 10
5 is less than 10

continue Statement

The continue statement is used to skip the current iteration, and continue with the next.

Example:

i = 0
while i < 5:
 i = i + 1
 if i == 2:
  continue
 print(i)

Output:

1
3
4
5

for loop

for loop is used to execute a set of statements each item in the sequence, that is either a list, a Dictionary, a set or a string.

Syntax:

for iterating_var in sequence:
   statements

Example:

num = [1, 2, 3, 4, 5, 6, 7]
for i in num:
 print(i)

Output:

1
2
3
4
5
6
7

range() Function

Range function returns a sequence of numbers it starts with o and increase by 1 until the special number is reached.

Example:

for i in range(5):
 print(i)

Output:

0
1
2
3
4

Nested loops

Python allow us to use one loop inside another loop.

Nested for loop

The general syntax for for loop is,

Syntax:

for iterating_var in sequence:
   for iterating_var in sequence:
      statements
   statements

Example:

for i in range(1, 8):
        for j in range(i):
            print("#",end=' ')
        print()

Output:

#
# #
# # #
# # # #
# # # # #
# # # # # #
# # # # # # #

Nested while loop

The general syntax for nested while loop is,

Syntax:

while expression:
   while expression:
      statement
   statement

Example:

a = 1
while(a <= 2):
 b = 1
 while(b <= 2):
  print(b)
  b = b+1
 print("\n")
 a = a + 1

Output:

1
2


1
2