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Enumerate and Zip

If we are coming from C, we might be tempted to use a counter variable or range(len(list)) to access indices. In Python, we use enumerate() and zip() to handle these patterns more cleanly. Both functions return iterators, making them memory efficient.

Enumerate: Iterating with an Index​

enumerate() adds a counter to an iterable, returning (index, item). Use it when we need the value and its position in the list.

tech_stack = ["Python", "C", "Bash"]

# start=1 makes the index start at 1 instead of 0
for idx, name in enumerate(tech_stack, start=1):
    print(f"{idx}. {name}")

Output:

1. Python
2. C
3. Bash

Why Not Use range(len())?​

Writing for i in range(len(list)): print(list[i]) is considered an anti-pattern in Python. It's slower, more verbose, and prone to errors. enumerate() is the "Pythonic" way to get indices.

Zip: Parallel Iteration​

zip() pairs up elements from multiple iterables, returning tuples. Use it when we have related data stored in separate lists.

users = ["Alice", "Bob", "Charlie"]
roles = ["Admin", "Editor", "Guest"]

for name, role in zip(users, roles):
    print(f"{name} is an {role}")

Output:

Alice is an Admin
Bob is an Editor
Charlie is an Guest

The "Shortest Wins" Rule​

zip() will silently stop as soon as the shortest input iterable is exhausted.

list_a = [1, 2, 3]
list_b = ["A", "B"]

# This only loops twice
for num, char in zip(list_a, list_b):
    print(num, char)

Output:

1 A
2 B