title: Adding Acces-Control-Allow-Origin to app.yml
body: <p>I'm following these instructions from Google App Engine docs :</p>
  
  <p><a href="https://cloud.google.com/appengine/docs/python/config/appref" rel="nofollow">https://cloud.google.com/appengine/docs/python/config/appref</a></p>
  
  <p>If you search for CORS, you'll see the example I am trying to copy. </p>
  
  <p>My app.yaml file looks like:</p>
  
  <pre><code>runtime: python27
  api_version: 1
  threadsafe: true
  
  handlers:
  - url: /.*
    script: main.app
    http_headers: Access-Control-Allow-Origin: *
  
  libraries:
  - name: ssl
    version: latest
  </code></pre>
  
  <p>However when I go to update it I get this error:</p>
  
  <pre><code>appcfg.py: error: Error parsing ./app.yaml: Unable to assign value 'Access-Control-Allow-Origin' to attribute 'http_headers':
  Value 'Access-Control-Allow-Origin' for http_headers is not of the expected type HttpHeadersDict
  </code></pre>
  
  <p>Why am I getting this error? What am I doing differently than the docs?</p>