python在类中调用plt.show()函数不显示

import matplotlib
gui_env = [i for i in matplotlib.rcsetup.interactive_bk]
non_gui_backends = matplotlib.rcsetup.non_interactive_bk
print ("Non Gui backends are:", non_gui_backends)
print ("Gui backends I will test for", gui_env)
for gui in gui_env:
    print ("testing", gui)
    try:
        matplotlib.use(gui,warn=False, force=True)
        from matplotlib import pyplot as plt
        print ("    ",gui, "Is Available")
        plt.plot([1.5,2.0,2.5])
        fig = plt.gcf()
        fig.suptitle(gui)
        plt.show()
        print ("Using ..... ",matplotlib.get_backend())
    except:
        print ("    ",gui, "Not found")

像这样直接调用就可以正常显示图像

而如果在类中调用函数就没有反应，这是为什么?

import matplotlib

class Novel():

    def __init__(self,name):
        self.name=name

    def draw(self):
        for gui in gui_env:
            print ("testing", gui)
        try:
            matplotlib.use(gui,warn=False, force=True)
            from matplotlib import pyplot as plt
            print ("    ",gui, "Is Available")
            plt.plot([1.5,2.0,2.5])
            fig = plt.gcf()
            fig.suptitle(gui)
            plt.show()
            print ("Using ..... ",matplotlib.get_backend())
        except:
            print ("    ",gui, "Not found")
test_1=Novel('test')
test_1.draw

像这样就毫无反应

类里面的try ... except是不是忘记缩进了？它们现在不在for循环内，应该不会被执行。
另外，test_1.draw()调用方法，原先是不是忘记加括号了。