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 get_snapshot(self, snapshot_id):
        """Returns the details of a single snapshot."""
        url = "snapshots/%s" % str(snapshot_id)
        resp, body = self.get(url)
        body = json.loads(body)
        return resp, body['snapshot']