def __init__(self, package, version):
        """Construct a new requirement.

        :param package: the package name.
        :param version: a semver compatible version specification.
        """
        self.package = package
        self.version = version
        if self.version and not re.match(r"[<=>~]", version[:2]):
            self.version = "=={}".format(self.version)
def exiter_as_until_exception(
        cls, new_exiter_fun: Callable[[Optional[Exiter]], Exiter]
    ) -> Iterator[None]:
        """Temporarily override the global exiter, except this will unset it when an exception
        happens."""
        previous_exiter = cls._exiter
        new_exiter = new_exiter_fun(previous_exiter)
        try:
            cls._reset_exiter(new_exiter)
            yield
        finally:
            cls._reset_exiter(previous_exiter)