'self' disappearing

Steven Taschuk staschuk at telusplanet.net
Sat Jul 5 23:44:02 CEST 2003


Quoth Daniel Nouri:
> The idea of my simple piece of code is to start from a given module and 
> wrap all functions and methods in that module and submodules. FunWrapper is 
> the class that I use for wrapping.
  [...]
> It appears that 'instance.method()' is not the same as 
> 'klass.method(instance)' in this case. But why? And how do I deal with 
> that?

Your function wrapper implements only the __call__ protocol; you
also need to handle the descriptor protocol, which is used to
implement the bound/unbound method business.  For example:

    class FunWrapper(object):
        def __init__(self, fun):
            self.fun = fun
        def __call__(self, *args, **kwds):
            print 'Calling', self.fun.__name__
            self.fun(*args, **kwds)
        def __get__(self, *args):
            print 'Getting', self.fun.__name__
            return FunWrapper(self.fun.__get__(*args))

    class Foo(object):
        def bar(*args):
            print 'called with args', args
        bar = FunWrapper(bar)

    foo = Foo()
    foo.bar('a', 'b', 'c')

You might find Raymond Hettinger's writeup of descriptors useful
to understand what's going on here:
    <http://users.rcn.com/python/download/Descriptor.htm>

-- 
Steven Taschuk                             staschuk at telusplanet.net
"I may be wrong but I'm positive."  -- _Friday_, Robert A. Heinlein





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