PyQt: how to handle event without inheritance

Question

How can I handle mouse event without a inheritance, the usecase can be described as follows:

Suppose that I wanna let the QLabel object to handel MouseMoveEvent, the way in the tutorial often goes in the way that we create a new class inherited from QLabel. But can I just use a lambda expression to handel the event without inheritance just like

ql = QLabel()
ql.mouseMoveEvent = lambda e : print e.x(), e.y()

So I do not need to write a whole class and just use simple lambda expression to implement some simple event.

ekhumoro · Accepted Answer · 2012-12-09 16:59:32Z

13

The most flexible way to do this is to install an event filter that can receive events on behalf of the object:

from PyQt4 import QtGui, QtCore

class Window(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.label = QtGui.QLabel(self)
        self.label.setText('Hello World')
        self.label.setAlignment(QtCore.Qt.AlignCenter)
        self.label.setFrameStyle(QtGui.QFrame.Box | QtGui.QFrame.Plain)
        self.label.setMouseTracking(True)
        self.label.installEventFilter(self)
        layout = QtGui.QVBoxLayout(self)
        layout.addWidget(self.label)

    def eventFilter(self, source, event):
        if (event.type() == QtCore.QEvent.MouseMove and
            source is self.label):
            pos = event.pos()
            print('mouse move: (%d, %d)' % (pos.x(), pos.y()))
        return QtGui.QWidget.eventFilter(self, source, event)

if __name__ == '__main__':

    import sys
    app = QtGui.QApplication(sys.argv)
    window = Window()
    window.show()
    window.resize(200, 100)
    sys.exit(app.exec_())

answered Dec 9, 2012 at 16:59

ekhumoro

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1 Comment

swdev Over a year ago

especially that installEventFilter(self)

mata · Accepted Answer · 2012-12-09 16:54:11Z

4

Yes you can do this, but in python2 you can't use print in your lambda, as it's a statement and not a function and does not return a value.

Try this:

ql = QLabel()
def event_handler(e):
    print e.x(), e.y()
ql.mouseMoveEvent = event_handler

answered Dec 9, 2012 at 16:54

mata

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2 Comments

user1006989 Over a year ago

print is a function in python3 from __future__ import print_function

mata Over a year ago

@X.Jacobs - of course, but from his print-syntax i figured he's using python2. of course a future import is also a solution for python2.6+.

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