Why does Google Search return HTTP Error 403?

Question

Consider the following Python code:

 30    url = "http://www.google.com/search?hl=en&safe=off&q=Monkey"
 31    url_object = urllib.request.urlopen(url);
 32    print(url_object.read());

When this is run, an Exception is thrown:

File "/usr/local/lib/python3.0/urllib/request.py", line 485, in http_error_default
   raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 403: Forbidden

However, when this is put into a browser, the search returns as expected. What's going on here? How can I overcome this so I can search Google programmatically?

Any thoughts?