title: TypeError : clean_country() takes exactly 1 argument (0 given)
body: <pre><code>class FilterForm(forms.Form):
      currency = forms.ChoiceField(choices=Currency_choices)
      continent = forms.ChoiceField(choices=Select_continent())   
      def clean_country(self):
          continent = self.cleaned_data['continent']
          result = Select_country(continent)
          return result 
      country = forms.ChoiceField(choices=clean_country()) //error is here
  </code></pre>
  
  <p>i'm trying to get the selected field in Continent and display al countries in that continent
  so try use clean_country which return a list fo countries in the selected continent.
  but i had TypeError : clean_country() takes exactly 1 argument (0 given)
  so how can i use this function?</p>