def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
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)