Coerce data from primitive form to native Python types.
        Returns the default type (if exists)

def to_python(self, value):
        '''
        Coerce data from primitive form to native Python types.
        Returns the default type (if exists)
        '''
        try:
            if value is None and self._default is not None:
                return self.default
            self._check_required(value)
            if not isinstance(value, self._python_type):
                value = self._import(value)
            return value
        except ValueError as ex:
            raise ValueError(ex, self._errors['to_python'])