api.py

class DynamicFormValidation(Validation):
    """ Validation class that allows dynamic form classes and initial data.

        Initial data is only used to validate the form - it will not modify
        the data that the user has posted. So form validation might pass,
        but saving the model will fail.
    """
    initial = {}

    def __init__(self, **kwargs):
        self.form_class = kwargs.get('form_class', None)

    def get_initial(self):
        return self.initial

    def get_form_class(self):
        """ Returns a Form class object.
        """
        if self.form_class:
            return self.form_class
        else:
            msg = ('You need to override get_form_class or pass a form_class '
                   'kwarg to DynamicFormValidation().')
            raise ImproperlyConfigured(msg)

    def get_form_kwargs(self, bundle):
        kwargs = {
            'initial': self.get_initial(),
            'data': self.data,
            'instance': bundle.obj
        }
        return kwargs

    def get_form(self, form_class):
        return form_class(**self.get_form_kwargs())

    def is_valid(self, bundle, request=None):
        self.data = bundle.data.copy()
        self.request = request

        form_class = self.get_form_class()

        if self.data is None:
            self.data = {}

        form = form_class(**self.get_form_kwargs(bundle))

        if form.is_valid():
            return {}

        return form.errors