If I do this:
def f(self): print self
class c1: pass
setattr(c1, 'm1', f)
Then f is automagically transmogrified into the appropriate sort of
method depending on how it is used:
>>> c1.m1
<unbound method c1.f>
>>> c1().m1
<bound method c1.f of <__main__.c1 instance at 0x51e738>>
>>> c1().m1()
<__main__.c1 instance at 0x51ec60>
Note that m1 gets passed a self argument.
The same automatic transmogrification does not happen if I use an
callable instance instead of an actual function object:
class callable:
def __call__(self, *args, **kw): return args, kw
>>> setattr(c1, 'm2', callable())
>>> c1.m2
<__main__.callable instance at 0x51e738>
>>> c1().m2
<__main__.callable instance at 0x51e738>
>>> c1().m2()
((), {})
Note that no selfarg has been passed to m2.
The reason I want to do this is that I want to implement a trace
facility that traces only specific class methods. I want to say:
trace(c1.m1)
and have c1.m1 be replaced with a wrapper that prints debugging info
before actually calling the old value of m1. The reason I want that to
be an instance of a callable class instead of a function is that I need
a place to store the old value of the method so I can restore it, and I
don't want to start building a global data structure because that gets
horribly ugly, and a callable class is the Right Thing -- if there's a
way to actually make it work.
Is there? I tried the obvious things (like making callable inherit from
function, and adding im_func and im_self attribuetes) but they didn't
work.
Thanks,
rg
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