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([10,2,5,8]) == [2,5,8,10]
  assert bubble_sort([7,3,2,1]) == [1,2,3,7]
  assert bubble_sort([1,1,1,1]) == [1,1,1,1]
  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]