input: from typing import List
  
  
  def bubble_sort(arr: List[int]):
      """ Sort a given list of integers in ascending order using bubble sort.
      >>> bubble_sort([3, 7, 4, 1])
      [1, 3, 4, 7]
      """
      n = len(arr)
      for i in range(n - 1):
          for j in range(0, n - i - 1):
              if arr[j] > arr[j + 1]:
                  arr[j], arr[j + 1] = arr[j + 1], arr[j]
output:     return arr