Python对象组合 - 从调用它的类访问方法

Question

You'll have to forgive me, I am trying to teach myself OO but I have come across this problem with composition and 'has-a' relationships.

class Main(object):
    def A(self):
        print 'Hello'
    def B(self):
        self.feature = DoSomething()

class DoSomething(object):
    def ModifyMain(self):
        #Not sure what goes here... something like
        Main.A()

def run():
    M = Main()
    M.B()

A real world example of the above simplification is a PySide application where Main is a MainWindow, and DoSomething is a dynamically created widget that is placed somewhere in the window. I would like DoSomething to be able to modify the status bar of the mainwindow, which is essentially calling (in Main) self.statusbar().

If there is a shortcut in PySide to do this, Tops!! please let me know! However, I'm actually after the more general Pythonic way to do this.

I think I'm close ... I just can't make it work...

Answer 1

Why don't you use a signal and slot instead? That's a more Qt and OOP way of doing this.

In your dynamically created widget class:

self.modifyMain = QtCore.Signal(str)

In your main class:

@QtCore.Slot(str)
def changeStatusbar(self, newmessage):
    statusBar().showMessage(newmessage)

in you main class after creating your widget:

doSomething.modifyMain.connect(self.changeStatusbar)

And in you widget class, where you want to change the statusbar of main, you say:

modifyMain.emit("Hello")

None of this is tested as I don't have a PySide installation handy.

Answer 2

There are two problems with your code:

1. At no time do you call ModifyMain ; and
2. Main.A() will result in an error, because A is an instance method, but you are calling it on a class .

You want something like:

class Main(object):
    def A(self):
        print 'Hello'
    def B(self):
        self.feature = DoSomething() # self.feature is an instance of DoSomething
        self.feature.ModifyMain(self) # pass self to a method

class DoSomething(object):
    def ModifyMain(self, main): # note that self is *this* object; main is the object passed in, which was self in the caller
        #Note case - main, not Main
        main.A()

def run():
    M = Main()
    M.B()

if __name__=="__main__": # this will be true if this script is run from the shell OR pasted into the interpreter
    run()

Your names all flout the usual python conventions found in PEP8 , which is a pretty good guide to python style. I have left them as they were in your code, but don't copy the style in this example - follow PEP8.