title: How to access context variables from the Jinja's Extension?
body: <p>I'm using django+jinja2 via coffin, and I can't understand how to access the context variables in the extension. For example, I have this:</p>
  
  <pre><code>from coffin.shortcuts import render_to_response
  
  def some_view(request):
      return render_to_response('template.html', {'a': 1})
  
  class RenderFooExtension(Extension):
      tags = set(['render_foo'])
  
      def parse(self, parser):
          lineno = parser.stream.next().lineno
  
          # Some parsing process
  
          return nodes.Output([self.call_method('render'),]).set_lineno(lineno)
  
      def render(self):
          # TODO: I need to get here, for example, `a` object
          return ''
  </code></pre>
  
  <p>So I need to get <code>a</code> variable in the <code>render</code> method. How can I do it?</p>