translate url with google translate from python script

I'm trying to use google translate from a python script:

#!/usr/bin/env python
from urllib2 import urlopen
from urllib import urlencode

base_url = "http://www.google.com/translate?"
params = (('langpair','en|es'), ('u','http://asdf.com'),)
url = base_url+urlencode(params)
print "Encoded URL: %s" % url 
print urlopen(url).read()

I'm getting the error 403 when I use it.

# ./1.py 
Encoded URL: http://www.google.com/translate?langpair=en%7Ces&u=http%3A%2F%2Fasdf.com
Traceback (most recent call last):
...
urllib2.HTTPError: HTTP Error 403: Forbidden

However, the same URL works fine when accessed from browser. Could anyone spot the error? Or is it that google does not allow this type of usage?

If Google doesn't let you do this, you could programatically translate the normal website's source via the Google's APIs.

I wrote a function for this a little while back:

def translate(text, src = '', to = 'en'):
  parameters = ({'langpair': '{0}|{1}'.format(src, to), 'v': '1.0' })
  translated = ''

  for text in (text[index:index + 4500] for index in range(0, len(text), 4500)):
    parameters['q'] = text
    response = json.loads(urllib.request.urlopen('http://ajax.googleapis.com/ajax/services/language/translate', data = urllib.parse.urlencode(parameters).encode('utf-8')).read().decode('utf-8'))

    try:
      translated += response['responseData']['translatedText']
    except:
      pass

  return translated