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 _files(self):
        if self.isexact():
            return [f for f in self._m1.files() if self(f)]
        # If m1 is not an exact matcher, we can't easily figure out the set of
        # files, because its files() are not always files. For example, if
        # m1 is "path:dir" and m2 is "rootfileins:.", we don't
        # want to remove "dir" from the set even though it would match m2,
        # because the "dir" in m1 may not be a file.
        return self._m1.files()