Loops (for / while)

Introduction

Python's for loop iterates over any iterable (list, dict, string, file, generator). while loops repeat until a condition is false.

Understanding the topic

Core concepts to understand:

• for x in iterable: — most common.
• range(n) for index loops.
• enumerate() for index + value.
• break, continue, else on loops.

Syntax reference

Visual flow / code:

# Iterate
for fruit in ["apple", "banana"]:
    print(fruit)

# Index + value
for i, name in enumerate(["a", "b"], start=1):
    print(i, name)

# Parallel iteration
for k, v in zip(["a", "b"], [1, 2]):
    print(k, v)

# while
n = 5
while n > 0:
    n -= 1

Execution workflow

Real-world use

Pythonic loops avoid C-style index loops. Use enumerate, zip, and comprehensions instead of for i in range(len(x)).

Best practices

• Iterate directly, not by index.
• Use enumerate when you need the index.
• Use zip for parallel iteration.

Common mistakes

• Modifying a list while iterating it — make a copy first.

Hands-on exercise

Interview preparation — practice these questions:

• for-else clause — what does it do?
• enumerate vs range(len)?
• When use while?

Summary

In summary: Iterate directly. enumerate + zip are everyday tools.