Class catch_threading_exception

src/_pytest/threadexception.py:15–57

Context manager catching threading.Thread exception using threading.excepthook. Storing exc_value using a custom hook can create a reference cycle. The reference cycle is broken explicitly when the context manager exits. Storing thread using a custom hook can resurrect it if it is

# Copied from cpython/Lib/test/support/threading_helper.py, with modifications.
class catch_threading_exception:
    """Context manager catching threading.Thread exception using
    threading.excepthook.

    Storing exc_value using a custom hook can create a reference cycle. The
    reference cycle is broken explicitly when the context manager exits.

    Storing thread using a custom hook can resurrect it if it is set to an
    object which is being finalized. Exiting the context manager clears the
    stored object.

    Usage:
        with threading_helper.catch_threading_exception() as cm:
            # code spawning a thread which raises an exception
            ...
            # check the thread exception: use cm.args
            ...
        # cm.args attribute no longer exists at this point
        # (to break a reference cycle)
    """

    def __init__(self) -> None:
        self.args: Optional["threading.ExceptHookArgs"] = None
        self._old_hook: Optional[Callable[["threading.ExceptHookArgs"], Any]] = None

    def _hook(self, args: "threading.ExceptHookArgs") -> None:
        self.args = args

    def __enter__(self) -> "catch_threading_exception":
        self._old_hook = threading.excepthook
        threading.excepthook = 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
        threading.excepthook = self._old_hook
        self._old_hook = None
        del self.args


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