def load(self, requirements_file=None):
        """Load or reload requirements from a requirements.txt file.

        :param requirements_file: if not given, the filename used from
            initialization will be read again.
        """
        if requirements_file is None:
            requirements_file = self.filename
            if requirements_file is None:
                raise ValueError("no filename provided")
        elif isinstance(requirements_file, text_type):
            requirements_file = Path(requirements_file)
        self.clear()
        with requirements_file.open() as f:
            self.loads(f.read())

        if isinstance(requirements_file, (text_type, Path)):
            self.filename = requirements_file
def exiter_as(cls, new_exiter_fun: Callable[[Optional[Exiter]], Exiter]) -> Iterator[None]:
        """Temporarily override the global exiter.

        NB: We don't want to try/finally here, because we want exceptions to propagate
        with the most recent exiter installed in sys.excepthook.
        If we wrap this in a try:finally, exceptions will be caught and exiters unset.
        """
        previous_exiter = cls._exiter
        new_exiter = new_exiter_fun(previous_exiter)
        cls._reset_exiter(new_exiter)
        yield
        cls._reset_exiter(previous_exiter)