Python Funktion als Variable aufrufen

#!/usr/bin/python3
import sys
def add(p1,p2):
  print (p1 + p2)
def sub(p1,p2):
  print (p1 - p2)
def mul(p1,p2):
  print (p1 * p2)
def dif(p1,p2):
  print (p1 % p2)

arg1 = int(sys.argv[1])
op = sys.argv[2]
arg2 = int(sys.argv[3])

if op in [ "add" ,"sub" ,"mul" ,"dif" ]:
  eval(op)(arg1,arg2)