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 _init_signals(self):
        """Initializes the backends and gtk signals """
        self.connect("cursor-changed", self.on_select_row)
        _signals = BackendSignals()
        _signals.connect(_signals.BACKEND_ADDED, self.on_backend_added)
        _signals.connect(_signals.BACKEND_STATE_TOGGLED,
                         self.on_backend_state_changed)