def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def __init__(self, backendsdialog):
        """
        Constructor, just initializes the gtk widgets

        @param backends: a reference to the dialog in which this is
        loaded
        """
        super().__init__()
        self.dialog = backendsdialog
        self.req = backendsdialog.get_requester()
        self._init_liststore()
        self._init_renderers()
        self._init_signals()
        self.refresh()