设置matplotlib图的父级

Question

我在设置由以下代码生成的数字时遇到问题。当主窗口关闭时它不会关闭。我在主窗口中使用了self.setAttribute（Qt.WA_DeleteonClose）。主窗口对象在调用smd函数时作为父对象传递。尽管我已经明确设置了canvas的父级，但是当关闭mainwindow时，生成的图形不会关闭。有什么原因？谢谢。

   def  smd(self,parent):
    from pylab import *
    import matplotlib

    from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas

    from matplotlib.backends.backend_qt4agg import NavigationToolbar2QTAgg as NavigationToolbar

    from matplotlib.figure import Figure
    import pylab as p

    sm = [1,2,3]
    fig = p.figure()

    ax = fig.add_subplot(111)
    ax.bar(range(len(sm)),sm,align='center')
    ax.set_xticks(range(len(sm)))


    canvas = FigureCanvas(fig)
    canvas.setParent(parent)
    #p.setParent(self)
    canvas.draw()
    fig.setParent(parent)
    print "parent is ", parent, canvas.parent()

    p.show()