def _clean_method(self):
    value = self.cleaned_data[field_name]
    if value:
        self.cleaned_data[get_double_name(field_name)] = value
    return value
def _clean_method(self):
    value = self.cleaned_data[field_name]
    if value:
        self.cleaned_data[get_double_name(field_name)] = value
    return value