Bagaimana saya bisa tahu jika mouse berada di atas widget?

Jika Anda ingin melacak kapan mouse masuk atau keluar dari widget, Anda dapat menggunakan sesuatu seperti ini:

#!/usr/bin/env python
#-*- coding:utf-8 -*-

from PyQt4 import QtCore, QtGui

class mainwindow(QtGui.QWidget):
    def __init__(self, parent=None):
        super(mainwindow, self).__init__(parent)

    def enterEvent(self, event):
        print "Mouse Entered"
        return super(mainwindow, self).enterEvent(event)

    def leaveEvent(self, event):
        print "Mouse Left"
        return super(mainwindow, self).enterEvent(event)

if __name__ == "__main__":
    import sys

    app  = QtGui.QApplication(sys.argv)
    main = mainwindow()
    main.show()
    sys.exit(app.exec_())

Jika Anda hanya ingin memeriksa apakah mouse berada di atas widget, Anda dapat menggunakan fungsi QWidget::underMouse ():

#!/usr/bin/env python
#-*- coding:utf-8 -*-

from PyQt4 import QtCore, QtGui

class mainwindow(QtGui.QWidget):
    def __init__(self, parent=None):
        super(mainwindow, self).__init__(parent)

        self.button = QtGui.QPushButton("Check Mouse in 3 seconds")
        self.button.clicked.connect(self.on_button_clicked)

        self.layout = QtGui.QHBoxLayout(self)
        self.layout.addWidget(self.button)

    def mouseReleaseEvent(self, event):  
        if self.underMouse():
            print "Do something"

        return super(mainwindow, self).mouseReleaseEvent(event)

    @QtCore.pyqtSlot()
    def on_button_clicked(self):    
        QtCore.QTimer.singleShot(3000, self.checkMouse)

    def checkMouse(self):
        print "Under Mouse: {0}".format(self.underMouse())

if __name__ == "__main__":
    import sys

    app  = QtGui.QApplication(sys.argv)
    main = mainwindow()
    main.show()
    sys.exit(app.exec_())

Metode lain akan melibatkan pemeriksaan apakah posisi mouse berada dalam geometri internal widget:

#!/usr/bin/env python
#-*- coding:utf-8 -*-

from PyQt4 import QtCore, QtGui

class mainwindow(QtGui.QWidget):
    def __init__(self, parent=None):
        super(mainwindow, self).__init__(parent)

        self.setMouseTracking(True)

    def mouseReleaseEvent(self, event):  
        posMouse =  event.pos()
        if self.rect().contains(posMouse):
            print "Under Mouse"

        return super(mainwindow, self).mouseReleaseEvent(event)

if __name__ == "__main__":
    import sys

    app  = QtGui.QApplication(sys.argv)
    main = mainwindow()
    main.show()
    main.resize(200, 200)
    sys.exit(app.exec_())

underMouse() adalah yang harus digunakan untuk menentukan apakah mouse Anda berada di atas widget.
Usage: widget.underMouse()
http://pyqt.sourceforge.net/Docs/PyQt4/qwidget.html#underMouse