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Diffstat (limited to '')
| -rw-r--r-- | tests/utils.py | 26 |
1 files changed, 25 insertions, 1 deletions
diff --git a/tests/utils.py b/tests/utils.py index 15fabbc2d0..a0ac11bc5c 100644 --- a/tests/utils.py +++ b/tests/utils.py @@ -15,7 +15,7 @@ import atexit import os -from typing import Any, Callable, Dict, List, Tuple, Union, overload +from typing import Any, Callable, Dict, List, Tuple, Type, TypeVar, Union, overload import attr from typing_extensions import Literal, ParamSpec @@ -341,3 +341,27 @@ async def create_room(hs: HomeServer, room_id: str, creator_id: str) -> None: context = await unpersisted_context.persist(event) await persistence_store.persist_event(event, context) + + +T = TypeVar("T") + + +def checked_cast(type: Type[T], x: object) -> T: + """A version of typing.cast that is checked at runtime. + + We have our own function for this for two reasons: + + 1. typing.cast itself is deliberately a no-op at runtime, see + https://docs.python.org/3/library/typing.html#typing.cast + 2. To help workaround a mypy-zope bug https://github.com/Shoobx/mypy-zope/issues/91 + where mypy would erroneously consider `isinstance(x, type)` to be false in all + circumstances. + + For this to make sense, `T` needs to be something that `isinstance` can check; see + https://docs.python.org/3/library/functions.html?highlight=isinstance#isinstance + https://docs.python.org/3/glossary.html#term-abstract-base-class + https://docs.python.org/3/library/typing.html#typing.runtime_checkable + for more details. + """ + assert isinstance(x, type) + return x |