Python While Loop

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Python While Loop is used to execute a block of statements repeatedly until a given condition is satisfied. When the condition becomes false, the line immediately after the loop in the program is executed.

In this example, the condition for while will be True as long as the counter variable (count) is less than 3. 

# Python example for while loop
count = 0
while (count < 3):
    count = count + 1
    print("Hello Geek")

Hello Geek
Hello Geek
Hello Geek

Let’s take a look at Python While Loop in detail:

while loop Syntax

while expression:
statement(s)

• condition: This is a boolean expression. If it evaluates to True, the code inside the loop will execute.
• statement(s): These are the statements that will be executed during each iteration of the loop.

While Loop Flowchart

While Loop

The while loop will continue running the code block as long as the condition evaluates to True. Each time the loop executes, the condition is checked again. If it is True, the loop continues; if it is False, the loop terminates, and the program moves to the next statement after the loop.

Infinite while Loop in Python

Here, the value of the condition is always True. Therefore, the body of the loop is run infinite times until the memory is full.

age = 28

# the test condition is always True
while age > 19:
    print('Infinite Loop')

Loop control statements change execution from their normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed. Python supports the following control statements.

while loop with continue statement

Python Continue Statement returns the control to the beginning of the loop.

# Prints all letters except 'e' and 's'
i = 0
a = 'geeksforgeeks'

while i < len(a):
    if a[i] == 'e' or a[i] == 's':
        i += 1
        continue
        
    print(a[i])
    i += 1

g
k
f
o
r
g
k

while loop with break statement

Python Break Statement brings control out of the loop.

# break the loop as soon it sees 'e'
# or 's'
i = 0
a = 'geeksforgeeks'

while i < len(a):
    if a[i] == 'e' or a[i] == 's':
        i += 1
        break
        
    print(a[i])
    i += 1

g

while loop with pass statement

The Python pass statement to write empty loops. Pass is also used for empty control statements, functions, and classes.

# An empty loop
a = 'geeksforgeeks'
i = 0

while i < len(a):
    i += 1
    pass
  
print('Value of i :', i)

Value of i : 13

while loop with else

As discussed above, while loop executes the block until a condition is satisfied. When the condition becomes false, the statement immediately after the loop is executed. The else clause is only executed when your while condition becomes false. If you break out of the loop, or if an exception is raised, it won’t be executed.

Note: The else block just after for/while is executed only when the loop is NOT terminated by a break statement. 

# Python program to demonstrate
# while-else loop

i = 0
while i < 4:
    i += 1
    print(i)
else:  # Executed because no break in for
    print("No Break\n")

i = 0
while i < 4:
    i += 1
    print(i)
    break
else:  # Not executed as there is a break
    print("No Break")

1
2
3
4
No Break

1

Python While Loop – FAQs

How to write while loop in Python?

A while loop in Python is created using the following syntax:

while condition:
    # code block to be executed

The loop runs as long as the condition is true.

What are typical use cases for using while loops in Python?

Typical use cases for while loops include:

• Repeating tasks until a condition is met, such as reading lines from a file.
• Continuously prompting the user for input until valid data is provided.
• Running the main loop of a game until the player quits.
• Polling or continuously checking the status of a resource or condition.

How to control a while loop with break and continue in Python?

break: Exits the loop immediately, regardless of the condition.

while True:
    s= input("Enter something (or 'quit' to stop): ")
    if s== 'quit':
        break
    print(f"You entered: {s}")

continue: Skips the rest of the code inside the loop for the current iteration and jumps back to the beginning to re-evaluate the condition.

cnt= 0
while cnt< 10:
    cnt+= 1
    if cnt% 2 == 0:
        continue
    print(cnt)  # prints only odd numbers

What are the dangers of using a while loop in Python?

The dangers include:

• Infinite Loops : If the condition never becomes false, the loop will run indefinitely, potentially causing the program to hang.
• Resource Exhaustion : Continuously running loops can consume system resources, such as memory and CPU, leading to performance issues.
• Complexity and Readability : While loops can make code harder to read and maintain if not used properly, especially when nested deeply or when the loop conditions are complex.

while True:
    print("This will run forever!")

How can we use a while loop to read user input in Python?

You can use a while loop to repeatedly prompt the user for input until a valid response is received:

s= ""
while s.lower() != "exit":
    s= input("Enter something (type 'exit' to stop): ")
    if s.lower() != "exit":
        print(f"You entered: {s}")
print("Goodbye!")

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Article Tags :

• Python
• python
• Python loop-programs
• python-basics

Practice Tags :

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