layout.addWidget(self.button)
self.setLayout(layout)

def plot(self):
    """ plot some random stuff """
data = [random.random() for i in range(10)]
ax = self.figure.add_subplot(111)
ax.hold(False)
ax.plot(data, '*-')
self.canvas.draw()
if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
main = Window()
main.show()
sys.exit(app.exec_())
How to embed matplotib in pyqt - for Dummies