Grep function in python

import os
import sys
import re

grep=sys.argv[1]
file=sys.argv[2]

def search(m):
        switch=re.search(r'%s' %grep, m)
        if switch:
                return m



f=open("%s" %file,"r")

for i in f.readlines():
        s=search(i)
        if s is not None:
                print s