While Logic

Overview

While loops run a block as long as a condition is true. They are ideal for event-driven loops, retries, game loops, and situations where you don't know the number of iterations in advance.

Syntax

python

# Basic while
count = 0
while count < 5:
    print(count)
    count += 1    # 0, 1, 2, 3, 4

# While with else (runs if loop ended normally, not via break)
n = 10
while n > 0:
    n -= 3
else:
    print("Loop ended")   # always runs

# Infinite loop with break
while True:
    user_input = input("Type 'quit' to exit: ")
    if user_input == "quit":
        break

Common Pitfalls

Always ensure the loop condition eventually becomes False or include a break — infinite loops block the thread.
Python's while/else runs the else clause only if the loop exits normally (no break) — useful for 'not found' search patterns.
Interview tip: Prefer for loops when the number of iterations is known; use while when looping until an event occurs.

Real-World Example

Retry logic with exponential backoff

example

python

import time

def fetch_with_retry(max_retries: int = 3) -> str:
    attempt = 0
    while attempt < max_retries:
        try:
            # Simulated flaky request
            if attempt < 2:
                raise ConnectionError("Timeout")
            return "Success!"
        except ConnectionError:
            attempt += 1
            wait = 2 ** attempt
            print(f"Retry {attempt}, waiting {wait}s")
            time.sleep(wait)
    return "Failed after retries"

print(fetch_with_retry())

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