List Comprehension Tasks in Python

List Comprehension Tasks in Python

List comprehension is one of Python’s most powerful and elegant features. It lets you create new lists from existing ones in a single, readable line of code.

Basic Syntax

# [expression for item in iterable if condition]
squares = [x**2 for x in range(10)]
print(squares)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

Squares of Even Numbers

even_squares = [x**2 for x in range(1, 11) if x % 2 == 0]
print(even_squares)  # Output: [4, 16, 36, 64, 100]

Filter Strings by Length

words = ["cat", "elephant", "dog", "hippopotamus", "ox"]
long_words = [w for w in words if len(w) > 4]
print(long_words)  # Output: ['elephant', 'hippopotamus']

Convert to Uppercase

fruits = ["apple", "banana", "cherry"]
upper_fruits = [f.upper() for f in fruits]
print(upper_fruits)  # Output: ['APPLE', 'BANANA', 'CHERRY']

Flatten a 2D List

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat = [num for row in matrix for num in row]
print(flat)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Dictionary Comprehension Bonus

nums = [1, 2, 3, 4, 5]
squared_dict = {n: n**2 for n in nums}
print(squared_dict)  # Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Key Takeaway

List comprehensions are faster than equivalent for-loops and more readable. Master the pattern [expression for item in iterable if condition] — it appears in almost every Python codebase.