10 Useful Python One-Liners

Python rewards clear and compact code. These ten one-liners solve common tasks in a single readable line. Each one is short enough to remember and useful enough to reach for often.

1. Reverse a List

Slicing with a negative step flips any sequence instantly.

nums = [1, 2, 3, 4]
print(nums[::-1])

2. Remove Duplicates

Turning a list into a set drops repeats, and wrapping it in sorted gives clean order.

items = [3, 1, 2, 3, 1]
print(sorted(set(items)))

3. Swap Two Variables

Python swaps values without a temporary variable.

a, b = 1, 2
a, b = b, a
print(a, b)

4. Sum of Squares

A generator expression inside sum keeps the math compact.

print(sum(x * x for x in range(1, 5)))

5. Flatten a Nested List

A comprehension with two loops merges rows into one list.

matrix = [[1, 2], [3, 4]]
print([x for row in matrix for x in row])

6. Count Word Frequency

Counter builds a tally from any sequence in one step.

from collections import Counter
print(Counter("banana"))

7. Merge Two Dictionaries

The double star unpacks both dictionaries into a new one.

a = {"x": 1}
b = {"y": 2}
print({**a, **b})

8. Find the Longest Word

The max function with a key picks the longest item.

words = ["cat", "elephant", "dog"]
print(max(words, key=len))

9. Create a Number List

A comprehension builds a list of even numbers quickly.

print([n for n in range(10) if n % 2 == 0])

10. Join a List Into Text

The join method turns a list of strings into one sentence.

parts = ["learn", "python", "fast"]
print(" ".join(parts))

Use Them Wisely

One-liners are powerful, but clarity always comes first. If a single line becomes hard to read, a normal block is the better choice. Try each example in the playground and keep the ones that make your code cleaner.