input: Write a function to sort a given array in ascending order using bubble sort.
  
  def bubble_sort(arr): 
      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] 
  
  assert bubble_sort([3, 7, 4, 1]) == [1, 3, 4, 7]
  assert bubble_sort([9, 5, 6, 2, 3]) == [2, 3, 5, 6, 9]
  assert bubble_sort([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
  assert bubble_sort([100, 25, 75, 50]) == [25, 50, 75, 100]
output: def bubble_sort(arr): 
      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]