another question on metaclasses

[Greg Chapman]

On 10 Dec 2002 11:01:17 -0800, mis6 at pitt.edu (Michele Simionato) wrote:

>i.e. what I want. Nevertheless, I wonder if there are cases where this script 
>could break down, then I ask the Python gurus for comments and feedback.

It may break if any of the Autoinit classes do not have an __init__ method:

class B(Autoinit):
    def __init__(self,*args,**kw):
        print "This is B.__init__"

class C(B):
    pass

class D(C):
    def __init__(self,*args,**kw):
        print "This is D.__init__"

d=D()

prints:

This is B.__init__
This is B.__init__
This is D.__init__

This is because cls.__init__ will return the nearest base class's __init__ if
cls does not itself define __init__.  Your meta __init__ should probably look
like:

    def __init__(cls,name,bases,dict):
        child_init=cls.__dict__.get('__init__')
        def double_init(self,*args,**kw):
            "Both the super and the child __init__ are called"
            super(cls,self).__init__(self,*args,**kw)
            if child_init:
                child_init(self,*args,**kw)
        setattr(cls,'__init__',double_init)

---
Greg Chapman