Python Data Mashup - geocode

Hi, I'm very new to python and am still learning so please bare with me.

I have this code:

import urllib, urllib2, re
import xml.etree.ElementTree as ET
from bs4 import BeautifulSoup

# The get_zipcode(address) function will be called with an address string with
# no zip code, such as 'Lowell Observatory, Flagstaff, AZ', and it should return the
# ZIP code of the address as a string
# For example, get_zipcode('Lowell Observatory, Flagstaff, AZ') should return '86001'
# Use the Google Geocoding API to obtain the ZIP code. Documentation:
# https://developers.google.com/maps/documentation/geocoding/
# Can use either json or xml output format. 
def get_zipcode(address):
  zipcode = ''
  # +++your code here+++
  url_values = urllib.urlencode(address)
  url="http://maps.googleapis.com/maps/api/geocode/json?address=%s&sensor=false" % address
  #return zipcode
  response = urllib2.urlopen(url)
  return response

I'm getting an error when I return response and I don't know why. Also, I'm not exactly if I am going about this the right way at all.