Class catch_unraisable_exception

src/_pytest/unraisableexception.py:15–59

Context manager catching unraisable exception using sys.unraisablehook. Storing the exception value (cm.unraisable.exc_value) creates a reference cycle. The reference cycle is broken explicitly when the context manager exits. Storing the object (cm.unraisable.object) can resurrect

# Copied from cpython/Lib/test/support/__init__.py, with modifications.
class catch_unraisable_exception:
    """Context manager catching unraisable exception using sys.unraisablehook.

    Storing the exception value (cm.unraisable.exc_value) creates a reference
    cycle. The reference cycle is broken explicitly when the context manager
    exits.

    Storing the object (cm.unraisable.object) can resurrect it if it is set to
    an object which is being finalized. Exiting the context manager clears the
    stored object.

    Usage:
        with catch_unraisable_exception() as cm:
            # code creating an "unraisable exception"
            ...
            # check the unraisable exception: use cm.unraisable
            ...
        # cm.unraisable attribute no longer exists at this point
        # (to break a reference cycle)
    """

    def __init__(self) -> None:
        self.unraisable: Optional["sys.UnraisableHookArgs"] = None
        self._old_hook: Optional[Callable[["sys.UnraisableHookArgs"], Any]] = None

    def _hook(self, unraisable: "sys.UnraisableHookArgs") -> None:
        # Storing unraisable.object can resurrect an object which is being
        # finalized. Storing unraisable.exc_value creates a reference cycle.
        self.unraisable = unraisable

    def __enter__(self) -> "catch_unraisable_exception":
        self._old_hook = sys.unraisablehook
        sys.unraisablehook = self._hook
        return self

    def __exit__(
        self,
        exc_type: Optional[Type[BaseException]],
        exc_val: Optional[BaseException],
        exc_tb: Optional[TracebackType],
    ) -> None:
        assert self._old_hook is not None
        sys.unraisablehook = self._old_hook
        self._old_hook = None
        del self.unraisable


def unraisable_exception_runtest_hook() -> Generator[None, None, None]: