Source code for molten.validation.forward

# This file is a part of molten.
# Copyright (C) 2018 CLEARTYPE SRL <[email protected]>
# molten is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or (at
# your option) any later version.
# molten is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# License for more details.
# You should have received a copy of the GNU Lesser General Public License
# along with this program.  If not, see <>.

import inspect
from typing import Any, no_type_check

def is_forward_ref(annotation: Any) -> bool:
    """Returns True when the given annotation is a forward ref.
    return issubclass(type(annotation), _forward_ref)

[docs]@no_type_check def forward_ref(name: str) -> Any: """Generate a proxy type for a schema that is going to be defined at some point after the current statement. Examples: Schema "A" includes a reference to a yet-to-be-defined schema "B":: @schema class A: b: forward_ref("B") @schema class B: x: int ``forward_ref`` can be used as a type parameter to other types as well:: @schema class A: b: List[forward_ref("B")] @schema class B: x: int Parameters: name: The name of the schema being referenced. This name must eventually be bound in the scope of the call site. """ try: caller_frame_info = inspect.stack()[1] return _forward_ref(f'_forward_ref("{name}")', (object,), { "_schema": None, "_name": name, "_namespace": caller_frame_info.frame.f_globals, }) finally: del caller_frame_info
class _forward_ref(type): @no_type_check def lookup(cls): schema = cls._schema if schema is None: schema = cls._schema = cls._namespace[cls._name] del cls._name del cls._namespace return schema