Lists

How to iterate a list in Python

Quick answer

Use `for item in lst`. When you need the index too, use enumerate(lst).

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)

for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

The bare `for item in lst` is the Python idiom — never write `for i in range(len(lst)): item = lst[i]`. It's harder to read and slower because of the double lookup.

When you DO need the index, enumerate() gives you both without the boilerplate. It defaults to 0-based; pass start=1 if you want 1-based like line numbers or lesson numbers.

Parallel iteration over multiple lists uses zip: `for name, age in zip(names, ages)`. If the lists might differ in length, use itertools.zip_longest — plain zip silently stops at the shortest input.

Variations

Index AND value with enumerate

for i, name in enumerate(["Alice", "Bob"], start=1):
    print(f"{i}. {name}")

start= controls the first index.

Two lists in lockstep

names = ["Alice", "Bob"]
ages = [30, 25]
for name, age in zip(names, ages):
    print(name, age)

zip is your friend — never write parallel index-loops.

Modify while iterating (copy first!)

nums = [1, 2, 3, 4]
for n in nums[:]:      # slice = copy
    if n % 2 == 0:
        nums.remove(n)

Never mutate the same list you're iterating — behaviour is undefined.

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