#! c:/Python26/python.exe
# -*- coding: utf-8 -*-

def double_it(x):
   return x*2

def test(num_1,num_2,operation=1):
  if operation == 1:
    print "adding"
    print num_1 + num_2
  elif operation == 2:
    print "subtracting"
    print num_1 - num_2
  elif operation == 3:
    print "multiply"
    print num_1 * num_2
  elif operation == 4:
    print "division"
    print num_1 / num_2
  else:
    print "unknow operation"

test(100,10,4)
xx=double_it(124)
print xx
print double_it(56.4)


-------------------------------output---------------------

$ python function.py
division
10
248
112.8