Bubble Sort Implementation in Python 3

Question

I have implemented a Bubble Sort. It works well. But if you think something needs to be improved, say it. This code was tested in Python 3.7.4.

def bubble_sort(nums):
 for i in range(len(nums)-1):
 for j in range(0,len(nums)-1-i,1):
 if nums[j] > nums[j+1]:
 swap(nums, j, j+1)
 return nums
def swap(nums, i, j):
 temp = nums[i]
 nums[i] = nums[j]
 nums[j] = temp
if __name__ == "__main__":
 a = [0,0,0,-1,-0,1,2,3,2,1]
 print(bubble_sort(a))

• Marek: Also you have to be aware that you modify the a list - this may not be intended. You might want to copy a list or create a new one and fill with results. stackoverflow.com/questions/2612802/how-to-clone-or-copy-a-list

Answer 1

Unnecessary Function

Your swap function is unnecessary. Simply replace the function call with this line:

nums[j], nums[j + 1] = nums[j + 1], nums[j]

This does the swapping for you.

Spacing

There should be spaces between values in lists

[1, 2, 3, 4, 5]

between numbers/strings and operators

if nums[j] > nums[j + 1]

and between parameters in a function call

for j in range(0, len(nums) - 1 - i, 1):

Type Hints

Your function header can look like this:

from typing import List, Union
def bubble_sort(nums: List[Union[int, float]]) -> List[Union[int, float]]:

What this says is that the function accepts a list of integers/floats, and returns a list of integers/floats. It adds another layer of descriptiveness to your code.

Docstrings

You should include a docstring at the beginning of every class/method/module you write. This allows you to describe in words what your code is doing.

def bubble_sort(nums: List[Union[int, float]]) -> List[Union[int, float]]:
 """
 A bubble sort algorithm, etc etc etc
 :param nums -> List: A list of integers/floats to sort
 :return List: The sorted list of integers/floats, from smallest -> biggest
 """

Answer 2

In addition to Linny's answer, one can also optimize the bubble sort algorithm like this:

def bubble_sort(nums): # sorry that I am too lazy to include type hints here :)
 for i in range(len(nums) - 1):
 found = False
 for j in range(len(nums) - 1 - i): # start == 0 and step == 1 are unnecessary
 if nums[j] > nums[j + 1]:
 nums[j], nums[j + 1] = nums[j + 1], nums[j]
 found = True # it means that there is at least a swap
 if not found: # if there is no swap it means that there is no need to go for next value of i
 break
 return nums

Hope it helps.