def repr_vars(self):
        """Return a dictionary the field definition

        Should contain all fields that are required for the definition of this field in a pyschema class"""
        d = OrderedDict()
        d["nullable"] = repr(self.nullable)
        d["default"] = repr(self.default)
        if self.description is not None:
            d["description"] = repr(self.description)
        return d