Steven D'Aprano wrote:
> Here's a simple class-factory function that returns a sub-class of the
> old-style class it is passed.
>
> def verbosify_oclass(klass):
> """Returns a verbose sub-class of old-style klass."""
> class VClass(klass):
> def __init__(self, *args, **kwargs):
> print "Calling initializer __init__ ..."
> klass.__init__(self, *args, **kwargs)
> return VClass
>
>
> Here it is in action:
>
>>>> class Parrot:
> ... def __init__(self, colour): self.colour = colour
> ...
>>>> VParrot = verbosify_oclass(Parrot)
>>>> bird = VParrot('red')
> Calling initializer __init__ ...
>>>> bird.colour
> 'red'
>
>
> Here's an equivalent for new-style classes. It uses super() because I
> understand that super() is preferred to calling the super-class by name.
>
>
> def verbosify_nclass(klass):
> """Returns a verbose sub-class of new-style klass."""
> class VClass(klass):
> def __new__(cls, *args, **kwargs):
> print "Calling constructor __new__ ..."
> return super(klass, cls).__new__(cls, *args, **kwargs)
> def __init__(self, *args, **kwargs):
> print "Calling initializer __init__ ..."
> super(klass, self).__init__(*args, **kwargs)
> return VClass
>
>
>
> But it doesn't work:
>
>>>> vint = verbosify_nclass(int)
>>>> vint(42)
> Calling constructor __new__ ...
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "<stdin>", line 6, in __new__
> TypeError: object.__new__(VClass) is not safe, use int.__new__()
>
>
> What am I doing wrong?
Why would you skip VClass in the super() calls? This should work:
def verbosify_nclass(klass):
"""Returns a verbose sub-class of new-style klass."""
class VClass(klass):
def __new__(cls, *args, **kwargs):
print "Calling constructor __new__ ..."
return super(VClass, cls).__new__(cls, *args, **kwargs)
def __init__(self, *args, **kwargs):
print "Calling initializer __init__ ..."
super(VClass, self).__init__(*args, **kwargs)
return VClass
Peer
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