title: AssertionError: No api proxy found for service "urlfetch"
body: <p>I am using <code>stripe</code> API to talk to Stripe services. Google AppEngine doesn't even get imported or involved here, but I am seeing this weird <code>AssertionError</code> related to GAE libraries. Below is the stacktrace. What could possibly go wrong?</p>
  
  <pre><code>$ python stripe_export.py 
  Traceback (most recent call last):
    File "stripe_export.py", line 99, in &lt;module&gt;
      etl_customers()
    File "stripe_export.py", line 72, in etl_customers
      customers = fetch_data(stripe.Customer)
    File "stripe_export.py", line 54, in fetch_data
      _list_obj = cls.all(limit=page_size)
    File "/Library/Python/2.7/site-packages/stripe/resource.py", line 332, in all
      response, api_key = requestor.request('get', url, params)
    File "/Library/Python/2.7/site-packages/stripe/api_requestor.py", line 140, in request
      method.lower(), url, params, headers)
    File "/Library/Python/2.7/site-packages/stripe/api_requestor.py", line 249, in request_raw
      method, abs_url, headers, post_data)
    File "/Library/Python/2.7/site-packages/stripe/http_client.py", line 160, in request
      payload=post_data
    File "/usr/local/google_appengine/google/appengine/api/urlfetch.py", line 268, in fetch
      rpc = create_rpc(deadline=deadline)
    File "/usr/local/google_appengine/google/appengine/api/urlfetch.py", line 224, in create_rpc
      return apiproxy_stub_map.UserRPC('urlfetch', deadline, callback)
    File "/usr/local/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 414, in __init__
      self.__rpc = CreateRPC(service, stubmap)
    File "/usr/local/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 68, in CreateRPC
      assert stub, 'No api proxy found for service "%s"' % service
  AssertionError: No api proxy found for service "urlfetch"
  </code></pre>