Python：嵌套类继承 [英] Python: Nested Class Inheritance

问题描述

从Base（super？）类声明一个子类的实例是可以的，因为我在这里：

Would it be OK to declare an instance of the sub-classed class from its Base (super?) class as I do it here:

if 'classB_args' in dictArg.keys() and dictArg['classB_args']:
    self['classB']=ClassA( dictArg['classB_args'] )

这样做有没有任何副作用？前进之前我应该​​注意什么。我有一种感觉迟早会发生什么问题...用cPickle，pickle或者可能是一个PyQt拖和下降？如果是，那么为什么会出现问题？

Are there any side effects of doing so? What should I be aware before moving forward. I have a feeling sooner or later something would go wrong... with cPickle , pickle or may be it would be a PyQt drag-and-dropt?.. if so then why would the problem arise?

class Base(dict):
    def __init__(self, *args, **kwargs):
        super(Base, self).__init__(*args, **kwargs)
        self.setdefault('id', -1)
        self.setdefault('name', None)
        self.setdefault('classB', None)

        if not args or len(args)==0: return
        dictArg=args[0]

        if 'classB_args' in dictArg.keys() and dictArg['classB_args']:
            self['classB']=ClassA( dictArg['classB_args'] )

    def getClassB(self):
        return self['classB']

class ClassA(Base):
    def __init__(self, *args, **kwargs):
        if not (args or kwargs):   raise Exception('you need to give me *something*!')
        super(ClassA, self).__init__(*args, **kwargs)
        self.setdefault('win', None)
        self.setdefault('mac', None)

myDictArg= {'id':1, 'name':'MyName', 'win':'c:/windows', 'mac': '/Volumes/mac/', 'classB_args': {'id':1, 'name':'MyProject'}}

myInstance=ClassA(myDictArg)
print myInstance.getClassB()

推荐答案

工作，答案是肯定的，但我不能想到这是一个好主意的情况。原因是，这锁定你的基类，真正只有有用的 ClassA ...我认为解决方案可能会更干净，做一些像：

If you're asking whether it will work, the answer is yes, but I can't think of a situation where it is a good idea. The reason is that this locks your base class down to being really only useful with ClassA ... I think that the solution would probably be cleaner to do something like:

myDictArg = {'id':1, 'name':'MyName', 'win':'c:/windows', 'mac': '/Volumes/mac/', 'classB': ClassA(id=1, name='MyProject')}

并放弃 Base .__ init __ 中的所有额外 classB_args 它更明确，所以用户最终知道什么期望。

and forgo all of the extra classB_args craziness in Base.__init__. It's more explicit so the user ends up knowing what to expect.

如果你真的不喜欢，你可以使用 self 的类型来决定使用什么比直接指定 更好的 ClassA ：

If you really don't like that, you could use the type of self to determine what to use rather than specifying ClassA directly which is a little better:

self['classB'] = type(self)(dictArg['classB_args'])

现在，如果从 Base 中派生一个新类，将会改为：

Now, if you derive a new class from Base, that will be used instead:

class Foo(Base): pass

instance = Foo(myDictArg)
print type(instance.getClassB())  # Foo !

---

---

a few other non-related points.

1. 不要在dct.keys（）中执行 x - 可怕在python2.x中无效。 c>


2. 一般来说，编写简单的包装器如 getClassB 被认为是unpythonic。


3. 您可以重写 if 子句来清除它：

1. Don't do x in dct.keys() -- It's horribly inefficient in python2.x. You can just do x in dct :-).
2. Generally speaking, writing simple wrappers like getClassB are considered "unpythonic". You can just access the data directly in python.
3. You can rewrite the if clause to clean it up a little:

如下：

   if 'classB_args' in dictArg.keys() and dictArg['classB_args']:
        self['classB']=ClassA( dictArg['classB_args'] )

转到：

   # with this, you can remove the `self.setdefault('classB', None)` statement.
   item = dictArg.get('classB_args')
   self['classB'] = type(self)(item) if item else item

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