title: django-filter: Using ChoiceFilter with choices dependent on request
body: <p>I am using django-filter and need to add a <code>ChoiceFilter</code> with choices dependent on the request that I receive. I am reading the docs for ChoiceFilter but it says: <code>This filter matches values in its choices argument. The choices must be explicitly passed when the filter is declared on the FilterSet</code>.</p>
  
  <p>So is there any way to get request-dependent choices in the <code>ChoiceFilter</code>?</p>
  
  <p>I haven't actually written the code but the following is what I want -</p>
  
  <pre><code>class F(FilterSet):
      status = ChoiceFilter(choices=?) #choices depend on request
      class Meta:
          model = User
          fields = ['status']
  </code></pre>