Alex Spinov

Posted on Mar 25

12 Python One-Liners That Will Make Your Code Shorter (And More Readable)

#python #productivity #beginners #discuss

I review a lot of Python code. The difference between a junior and a senior often comes down to knowing these patterns.

Here are 12 one-liners I use almost daily.

1. Flatten a List of Lists

# Instead of:
result = []
for sublist in nested:
    for item in sublist:
        result.append(item)

# One-liner:
result = [item for sublist in nested for item in sublist]

2. Swap Two Variables

a, b = b, a

No temp variable needed. Python handles this elegantly.

3. Merge Two Dictionaries

merged = {**dict1, **dict2}

# Python 3.9+
merged = dict1 | dict2

If keys overlap, the second dict wins.

4. Read a File Into a List of Lines

lines = open('file.txt').read().splitlines()

5. Find the Most Common Element

from collections import Counter
most_common = Counter(my_list).most_common(1)[0][0]

Works with strings, numbers, any hashable type.

6. Reverse a String

reversed_str = my_string[::-1]

The [::-1] slice works on lists too.

7. Check if All Elements Meet a Condition

# Are all scores passing?
all_pass = all(score >= 60 for score in scores)

# Does any score fail?
any_fail = any(score < 60 for score in scores)

8. Create a Dictionary From Two Lists

keys = ['name', 'age', 'city']
values = ['Alex', 30, 'Berlin']
person = dict(zip(keys, values))

9. Remove Duplicates While Preserving Order

unique = list(dict.fromkeys(my_list))

This preserves insertion order (Python 3.7+). Using set() loses order.

10. Transpose a Matrix

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
transposed = list(zip(*matrix))

11. Filter and Transform in One Step

# Get squares of even numbers only
result = [x**2 for x in numbers if x % 2 == 0]

12. Pretty-Print JSON

import json
print(json.dumps(data, indent=2, ensure_ascii=False))

The ensure_ascii=False part is crucial if you work with non-English text.

The One Rule I Follow

One-liners should make code MORE readable, not less. If a one-liner takes 30 seconds to understand, use 3 lines instead.

The goal is clarity, not cleverness.

What is your favorite Python one-liner?

I bet there are patterns I missed. Share your most-used one-liner in the comments and I will add the best ones to this list with credit.

I write about Python, web scraping, and developer productivity. Follow for weekly practical tips.

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