50 Most Useful Python One-Liners Every Developer Should Know

Python is well-known for its clean syntax and powerful one-liners. Whether you’re building scripts, automating tasks, or crunching data, Python one-liners can help you write concise, readable, and efficient code.

In this article, we’ll explore 50 practical Python one-liners that every developer should know—categorized by use case so you can find exactly what you need, fast.

List and Comprehension One-Liners

1. Create a list of numbers from 0 to 9

nums = [x for x in range(10)]

2. Get squares of even numbers from 0 to 9

squares = [x**2 for x in range(10) if x % 2 == 0]

3. Flatten a 2D list

flat = [item for sublist in matrix for item in sublist]

4. Reverse a list

rev = my_list[::-1]

5. Remove duplicates from a list

unique = list(set(my_list))

6. Sort a list of tuples by second element

sorted_list = sorted(my_list, key=lambda x: x[1])

7. Get common elements in two lists

common = list(set(list1) & set(list2))

8. Get difference between two lists

diff = list(set(list1) - set(list2))

String Manipulation One-Liners

9. Reverse a string

reversed_str = my_str[::-1]

10. Check if a string is a palindrome

is_palindrome = s == s[::-1]

11. Count vowels in a string

vowel_count = sum(c in 'aeiouAEIOU' for c in s)

12. Remove all vowels from a string

no_vowels = ''.join(c for c in s if c.lower() not in 'aeiou')

13. Capitalize first letter of each word

pythonCopyEditcapitalized = ' '.join(w.capitalize() for w in s.split())

14. Find frequency of characters

pythonCopyEditfrom collections import Counter
freq = Counter(s)

Dictionary and Set One-Liners

15. Swap keys and values in a dictionary

swapped = {v: k for k, v in d.items()}

16. Merge two dictionaries (Python 3.9+)

pythonCopyEditmerged = dict1 | dict2

17. Get keys with value greater than 10

filtered_keys = [k for k, v in d.items() if v > 10]

18. Check for duplicate values in dictionary

has_duplicates = len(set(d.values())) < len(d.values())

19. Filter dictionary by condition

filtered = {k: v for k, v in d.items() if v % 2 == 0}

Functional Programming One-Liners

20. Sum of squares using map() and sum()

total = sum(map(lambda x: x**2, range(10)))

21. Filter odd numbers

odds = list(filter(lambda x: x % 2 == 1, range(10)))

22. Convert list of strings to uppercase

upper = list(map(str.upper, words))

23. Get length of each word

lengths = list(map(len, words))

24. Check if all elements are positive

all_positive = all(x > 0 for x in nums)

25. Check if any element is zero

has_zero = any(x == 0 for x in nums)

File Handling One-Liners

26. Read a file into a list of lines

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

27. Write list to file

open('file.txt', 'w').writelines('\n'.join(lines))

28. Count lines in a file

line_count = sum(1 for _ in open('file.txt'))

29. Get all words in a file

words = open('file.txt').read().split()

30. Find all lines containing a keyword

matches = [line for line in open('file.txt') if 'error' in line]

Numeric and Math One-Liners

31. Check if number is prime

is_prime = lambda n: n > 1 and all(n % i for i in range(2, int(n**0.5)+1))

32. Calculate factorial

from math import factorial
f = factorial(5)

33. Calculate GCD of two numbers

from math import gcd
g = gcd(48, 18)

34. Find max without using max()

m = sorted(nums)[-1]

35. Round a number to 2 decimal places

rounded = round(num, 2)

Date and Time One-Liners

36. Get current date and time

from datetime import datetime
now = datetime.now()

37. Get today’s date

from datetime import date
today = date.today()

38. Calculate days between dates

delta = (date2 - date1).days

39. Format date as string

formatted = datetime.now().strftime('%Y-%m-%d')

40. Parse date string

parsed = datetime.strptime('2025-07-06', '%Y-%m-%d')

Miscellaneous One-Liners

41. Generate a list of random numbers

import random
randoms = [random.randint(1, 100) for _ in range(10)]

42. Get environment variable

import os
val = os.getenv('HOME')

43. Check if a file exists

import os
exists = os.path.exists('file.txt')

44. Create a list of tuples (index, value)

indexed = list(enumerate(my_list))

45. Shuffle a list

random.shuffle(my_list)

46. Zip two lists

zipped = list(zip(list1, list2))

47. Unzip a list of tuples

a, b = zip(*zipped)

48. Generate all combinations of a list

from itertools import combinations
combos = list(combinations(my_list, 2))

49. Print a formatted string

print(f"Hello, {name}!")

50. Run a simple HTTP server

python -m http.server

Final Thoughts

Python one-liners are not just clever tricks—they’re time-savers, code simplifiers, and productivity boosters. Whether you’re writing scripts, solving coding challenges, or building real-world applications, mastering these one-liners can help you write cleaner and more efficient code.

Start incorporating these into your projects, and over time, they’ll become second nature in your Python toolkit.