code: def _generate_signature(self, base_url, private_key):
          
          url = urlparse.urlparse(base_url)
          url_to_sign = url.path + '?' + url.query
          decoded_key = base64.urlsafe_b64decode(private_key)
          signature = hmac.new(decoded_key, url_to_sign, hashlib.sha1)
          return base64.urlsafe_b64encode(signature.digest())
docs: http://code.google.com/apis/maps/documentation/webservices/index.html#PythonSignatureExample