子类tkinter中的super()在python中不起作用

Question

我有一个类，叫做 Application，它有两个子类，分别是 MyButton 和 MyLabel。Application 里面还有一些东西

self.backgroundcolor = 'orange'
self.textcolor = 'black'

我想在我的子类 MyButton 和 MyLabel 中使用这两个变量。所以，我试着这样做

class MyButton(Button):
    def __init__(self, *args, **kwargs):
        Button.__init__(self, *args, **kwargs)
        self['bg'] = super(Application, self).backgroundcolor
        self['fg'] = super(Application, self).textcolor
        self['relief'] = FLAT

class MyLabel(Label):
    def __init__(self, *args, **kwargs):
        Label.__init__(self, *args, **kwargs)
        self['fg'] = super(Application, self).textcolor

但是不行，系统提示说

TypeError: super(type, obj): obj must be an instance or subtype of type

不过我的 Application 类看起来是这样的

class Application(Frame):
    global yearcal
    def __init__(self, master=None):
        Frame.__init__(self, master)
        self.month = 5
        self.year = 2014
        self.color_clicked = 'lightskyblue'
        now = datetime.datetime.now()
        self.thisyear = now.year
        self.thismonth = now.month
        self.today = now.day
        self.textcolor = 'purple'
        self.bgcolor = 'gray'
        self.today_color = 'palegreen1'
        self.apt_color = 'light coral'
    MORE STUFF HERE...

    class MyButton(Button):
        def __init__(self, *args, **kwargs):
            Button.__init__(self, *args, **kwargs)
            self['bg'] = super(Application, self).backgroundcolor
            self['fg'] = super(Application, self).textcolor
            self['relief'] = FLAT

    class MyLabel(Label):
        def __init__(self, *args, **kwargs):
            Label.__init__(self, *args, **kwargs)
            self['fg'] = super(Application, self).textcolor

Answer 1

在这个例子中，有些混淆了嵌套类和子类的概念。嵌套类是指在另一个类里面定义的类，而子类是通过扩展一个已有的类来定义的。

在Python中，类的继承（也就是super方法的基础）是通过定义一个类，并把父类作为参数来实现的：

class Application(Frame):
    ... #Some class definition

class MyButton(Application):
    ... #MyButton is now a subclass of Application.

但是这并不是你想要的，因为你希望你的和类能够继承Tkinter的和类的行为，而不是继承类的行为。

你最开始尝试使用嵌套类并不一定是个坏主意，因为这样可以把你类的所有行为整齐地放在一个地方，但它有一些严重的缺点，可能不是你想要的。

首先，你不能在嵌套类中引用类的实例，除非你在某种情况下把它传进去，比如在初始化的时候。不过，如果这些属性是类中的类属性，你是可以访问的，就像你访问嵌套类一样。这可能有点让人困惑，下面是一个例子：

class Application(object):
    classvar = "Foo" #This is a class level variable

    class NestedClass(object):
        #This is now a nested class, accessed using Application.NestedClass
        def __init__(self, app):

            #This will fail, classvar doesn't exist in this scope
            self.var = classvar

            #This will work if app is an instance of Application
            #Or if app is the class itself
            self.var = app.classvar

            #This will always work, since it references the Application 
            #class directly but it won't capture changes introduced 
            #by an instance of Application, which is what you'll probably do
            self.var = Application.classvar

由于作用域的问题，类级别的行为会变得非常混乱，而嵌套类则会更加混乱，因为没有什么好处是通过在模块级别实现每个类可以获得的。

处理这种需求的最好方法就是按照自己做的方式来做。把实例作为它创建的控件实例的主控件传递。这在Marcin的回答中有说明。

Answer 2

在调用 super() 时，你需要传入你的 type 和“你自己”（self）：

super(Application, self)

所以不要这样做：

super(MyButton, self)

因此出现了这个错误，obj 必须是 type 的实例或子类型：
self 既不是 Application 的实例，也不是它的子类型。

Answer 3

我有一个类，叫做 Application，它有两个子类，分别是 MyButton 和 MyLabel。

MyButton 和 MyLabel 似乎并不是 Application 的子类。你只能通过 super() 来从子类访问 Application。

比如，要让 MyLabel 成为 Application 的子类，可以这样做：

class MyLabel(Application):
        def __init__(self, *args, **kwargs):
            ...

Answer 4

嵌套类不能直接访问外部类的属性。你需要通过间接的方式来访问，比如：

class Application(Frame):
    global yearcal
    def __init__(self, master=None):
        Frame.__init__(self, master)
        self.month = 5
        self.year = 2014
        self.color_clicked = 'lightskyblue'
        now = datetime.datetime.now()
        self.thisyear = now.year
        self.thismonth = now.month
        self.today = now.day
        self.textcolor = 'purple'
        self.bgcolor = 'gray'
        self.today_color = 'palegreen1'
        self.apt_color = 'light coral'

        # create button and label and pass the application instance 
        # so that they can reference its attributes and methods
        self.my_button = MyButton(self)
        self.my_label = MyLabel(self)



class MyButton(Button):
    def __init__(self, app_instance, *args, **kwargs):
        Button.__init__(self, *args, **kwargs)

        self['bg'] = app_instance.backgroundcolor
        self['fg'] = app_instance.textcolor

        self['relief'] = FLAT

class MyLabel(Label):
    def __init__(self, app_instance, *args, **kwargs):
        Label.__init__(self, *args, **kwargs)

        self['fg'] = app_instance.textcolor