The immediate use case I can think of this for is to make it possible to just do:
__len__ = instancemethod(operator.attrgetter('_length')) __hash__ = instancemethod(operator.attrgetter('_cached_hash'))
and stuff like that. Mostly just a minor performance optimization to avoid the overhead of Python level function calls (and in the case of stuff like __hash__, reduce the probability of the GIL releasing during a dict/set operation, though you'd still need some way to move __eq__ to the C layer to allow stuff like setdefault to be truly atomic).
This was possible in Python 2 with types.MethodType (since it could make unbound methods of a class for you; unbound methods no longer exist). Now the solution is... considerably uglier (requires ctypes): https://stackoverflow.com/q/40120596/364696
On Sun, Sep 13, 2020 at 5:24 AM Steven D'Aprano email@example.com wrote:
On Sun, Sep 13, 2020 at 12:32:54AM -0400, Random832 wrote:
This isn't what I was suggesting - I meant something like this:
class instancemethod: def __init__(self, wrapped): self.wrapped = wrapped def __get__(self, obj, objtype): if obj is None: return self.wrapped else: return MethodType(self.wrapped, obj)
this wouldn't be useful for functions, but would give other callables the same functionality as functions, automatically creating the bound method object, e.g.:
class D: def __init__(self, obj, *args): ...
class C: foo = instancemethod(D)
You want a method which does absolutely nothing at all but delegate to a class constructor or callable object (but not a function), with no docstring and no pre-processing of arguments or post-processing of the result.
Seems like an awfully small niche for this to be in the stdlib.
But having said that, I might have a use for that too. Except... I would need a docstring. And pre- and post-processing. Hmmm.
Seems to me that this might be useful in theory, but in practice we might never use it, preferring this instead:
class C: def foo(self, *args): """Doc string.""" return D(self, *args)
with appropriate pre- and post-processing as needed.
Interesting suggestion though, I may have to play around with it.
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