class Signal:

    """Simple implementation of signal/slot concept.

    In signalling class, add attribute with "sig_" prefix:
        self.sig_clicked = Signal()

    In listening class, add normal method, e.g. "close()" and connect it, e.g:
        button.sig_clicked.connect(window.close)

    When button gets clicked, it should call the signal:
        self.sig_clicked()

    Then window.close() will be called.

    """

    def __init__(self):
        self._handlers = []

    def __call__(self, *args, **kwargs):
        """Emit the signal to all connected handlers."""
        for handler in self._handlers:
            handler(*args, **kwargs)

    def connect(self, handler):
        if not handler in self._handlers:
            self._handlers.append(handler)

    def disconnect(self, handler):
        self._handlers.remove(handler)