Loops in Python

Complete guide to Python loops: for loops, while loops, nested loops, break, continue, pass, else clauses, loop patterns, and choosing the right iteration strategy.

Introduction to Loops

A loop allows the same block of code to run multiple times automatically.

1. Why Loops Are Needed

Loops remove repetition.

for Loop

Python for loops iterate over sequences like range, lists, strings, etc.

1. Basic for Loop with range()

range(start, stop) generates numbers.

2. Traversing a List

Iterate directly over elements.

while Loop

while loops run until the condition becomes False.

1. Basic while Loop

Condition checked before each iteration.

Simulating do-while

Python does not have do-while, but it can be simulated.

1. Simulated do-while Pattern

Use while True with break.

Loop with Index (enumerate)

enumerate() provides index and value together.

1. Using enumerate()

Index + value iteration.

Looping Over Dictionaries

Dictionaries support multiple iteration styles.

1. Using items()

Key-value iteration.

break & continue

break exits loop. continue skips iteration.

1. break

Exit loop immediately.

2. continue

Skip current iteration.

Reverse Loop

range can step backwards using a negative step.

1. Reverse with range

Use negative step.

Guard Clauses in Loops

Guard clauses help keep loop bodies flat and readable by handling invalid cases early using continue or break.

1. Guard Clause using continue

Skip invalid data early instead of nesting logic.

Best Practices

Choosing the correct loop improves clarity, performance, and maintainability.

1. Loop Selection Guidelines

When to use which loop.

Best Practices

Choosing the correct loop improves clarity, prevents bugs, and makes logic easier to understand.

1. Loop Selection Guidelines

Clear rules for writing better loops.