input: def bubble_sort(arr):
      """
      Sorts a given array in ascending order using the bubble sort algorithm.
      >>> arr = [3, 7, 4, 1]
      >>> bubble_sort(arr)
      Sorted array:
      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] 
  
  arr = [3,7,4,1]
  bubble_sort(arr) 
  print ("Sorted array :") 
  for i in range(len(arr)): 
      print ("%d" %arr[i]),
output:     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] 
  
  arr = [3,7,4,1]
  bubble_sort(arr) 
  print ("Sorted array :") 
  for i in range(len(arr)): 
      print ("%d" %arr[i])