Powerful Python One Liners

Feb 20, 2021 · 2 mins read

Why write more code when you can write less? Become a Python Ninja with the below one-liners.

1. Swapping variables

a, b = b, a

2. Assigning multiple values

a, b, c = 10, 20, 30

3. Create a list

## Instead of this
nums = []
for i in range(10):
    nums.append(i)

## DO THIS
nums = [i for i in range(10)]

4. Take subset of a list

nums = [1, 2, 3, 4, 5, 6]
b = [num for num in nums if num%2 == 0]

5. Shorten if/else (with ternary operator)

## Instead of this
if age<20:
    print("Young")
else:
    print("Old")

## DO THIS
print("Young") if age<20 else print("Old")

6. Reverse a string/list

>>> s = "GMO"
>>> s[::-1]
"OMG"

7. Check palindrome

>>> s = "madam"
>>> s == s[::-1]
True

8. Take input in one line

## Instead of this
a = input()
b = input()
c = input()

## DO THIS
a, b, c = input().split(' ')

## If type casting is needed then, (from string to int)-
a, b, c = [int(x) for x in input().split(' ')]

9. Read a file

f = [line for line in open("filename")]

10. Generate groups

>>> groups = [(a, b) for a in ['a', 'b'] for b in [1, 2, 3]] 
>>> groups
[(a, 1), (a, 2), (a, 3), (b, 1), (b, 2), (b, 3)]

11. Generator expression

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

## Instead of this
def number_generator(list):
    for item in list:
        yield item

>>> g = number_generator(nums)
>>> next(g)
0

## DO THIS
>>> nums = [x for x in range(10)]
>>> g = (n for n in nums)
>>> next(g)
0

Conclusion

One-liners look cool and it does make code smaller. However, it might not be the best idea to always use them. One-liners can make code hard to read. Additionally, they might not always be the most memory efficient. If your code needs to be more readable/maintainable, avoid complex one-liners in favor of longer but readable code.