Nested while loop in Python | Example code

When a while loop is used inside another while loop then it is called nested while loop in Python. Python allows using one loop inside another loop.

while expression:             
         while expression:    
                 statement(s) 
statement(s)

The syntax for a nested while loop in Python is as follows:

outer_condition = True

while outer_condition:
    # Outer loop statements

    inner_condition = True

    while inner_condition:
        # Inner loop statements

        # Inner loop termination condition
        if some_condition:
            inner_condition = False

    # Outer loop termination condition
    if some_condition:
        outer_condition = False

1. Start by defining the outer condition, which determines whether the outer loop will continue executing. This condition is checked at the beginning of each iteration of the outer loop.
2. Begin the outer while loop, using the while keyword followed by the outer condition.
3. Within the body of the outer loop, you can include any desired statements or instructions.
4. Define the inner condition, which determines whether the inner loop will continue executing. This condition is checked at the beginning of each iteration of the inner loop.
5. Start the inner while loop using the while keyword followed by the inner condition.
6. Inside the body of the inner loop, you can include the statements or instructions specific to the inner loop.
7. If there is a specific condition that should terminate the inner loop before it has completed all iterations, you can include an if statement within the inner loop to check that condition and set the inner_condition to False if the condition is met.
8. If there is a specific condition that should terminate the outer loop before it has completed all iterations, you can include an if statement after the inner loop to check that condition and set the outer_condition to False if the condition is met.
9. The program will continue execution until either the inner condition or the outer condition evaluates to False, terminating the respective loop.

Remember to modify the code according to your specific requirements and conditions.

Example Nested while loop in Python

Simple example code.

i = 1
j = 5
while i < 4:
    while j < 8:
        print(i, ",", j)
        j = j + 1
        i = i + 1

Output:

Another example

Display multiplication table using nested while in Python language.

i = 1
while i <= 5:
    j = 1
    while j <= 5:
        print(i, "*", j, '=', i * j)
        j += 1
    i += 1
    print("\n")

Output:

1 * 1 = 1
1 * 2 = 2
1 * 3 = 3
1 * 4 = 4
1 * 5 = 5


2 * 1 = 2
2 * 2 = 4
2 * 3 = 6
2 * 4 = 8
2 * 5 = 10


3 * 1 = 3
3 * 2 = 6
3 * 3 = 9
3 * 4 = 12
3 * 5 = 15


4 * 1 = 4
4 * 2 = 8
4 * 3 = 12
4 * 4 = 16
4 * 5 = 20


5 * 1 = 5
5 * 2 = 10
5 * 3 = 15
5 * 4 = 20
5 * 5 = 25

Comment if you have any doubts or suggestions on this Python While loop program.

Note: IDE: PyCharm 2021.3.3 (Community Edition)

Windows 10

Python 3.10.1

All Python Examples are in Python 3, so Maybe its different from python 2 or upgraded versions.