input: Write a function to implement the bubble sort algorithm to sort a given array in ascending order.
  
  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([9,8,7,6,5]) == [5,6,7,8,9]
  assert bubble_sort([1,2,3,4,5]) == [1,2,3,4,5]
  assert bubble_sort([5,3,8,6,7,2]) == [2,3,5,6,7,8]
  assert bubble_sort([]) == []
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]