Firstly, you should get rid of the old-style signal syntax, and define a custom clicked
signal, like this:
class Text(QtGui.QLabel):
clicked = QtCore.pyqtSignal()
def mouseReleaseEvent(self, evt):
...
self.clicked.emit()
Then use a lambda
to send the argument with the signal:
self.a1.clicked.connect(lambda: self.OpenURL(url))
More information about new-style signal/slot syntax can be found here.