Class FailingResponder

invoke/watchers.py:113–145

Variant of `Responder` which is capable of detecting incorrect responses. This class adds a ``sentinel`` parameter to ``__init__``, and its ``submit`` will raise `.ResponseNotAccepted` if it detects that sentinel value in the stream. .. versionadded:: 1.0

class FailingResponder(Responder):
    """
    Variant of `Responder` which is capable of detecting incorrect responses.

    This class adds a ``sentinel`` parameter to ``__init__``, and its
    ``submit`` will raise `.ResponseNotAccepted` if it detects that sentinel
    value in the stream.

    .. versionadded:: 1.0
    """

    def __init__(self, pattern: str, response: str, sentinel: str) -> None:
        super().__init__(pattern, response)
        self.sentinel = sentinel
        self.failure_index = 0
        self.tried = False

    def submit(self, stream: str) -> Generator[str, None, None]:
        # Behave like regular Responder initially
        response = super().submit(stream)
        # Also check stream for our failure sentinel
        failed = self.pattern_matches(stream, self.sentinel, "failure_index")
        # Error out if we seem to have failed after a previous response.
        if self.tried and failed:
            err = 'Auto-response to r"{}" failed with {!r}!'.format(
                self.pattern, self.sentinel
            )
            raise ResponseNotAccepted(err)
        # Once we see that we had a response, take note
        if response:
            self.tried = True
        # Again, behave regularly by default.
        return response