Return appropriate input validator.

        For POST requests, ``self.post_representation`` is returned
        if it is present, ``self.representation`` otherwise.

def _get_input_validator(self, request):
        """ Return appropriate input validator.

        For POST requests, ``self.post_representation`` is returned
        if it is present, ``self.representation`` otherwise.
        """

        method = request.method.upper()
        if method != 'POST':
            return self.representation
        elif self.post_representation:
            return self.post_representation
        else:
            return self.representation