input: 
  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] 
  
  arr = [3,7,4,1]
  bubble_sort(arr) 
  print ("Sorted array :") 
  for i in range(len(arr)): 
      print ("%d" %arr[i]),
  
  # Output:
  # Sorted array :
  # 1 3 4 7
  
output:     return arr