New submission from Skip Montanaro:
I needed to create a partial method in Python 2.7, so I grabbed
functools.partialmethod from a Python 3.5.2 install. For various reasons, one
of the reasons I wanted this was to suck in some methods from a delegated class
so they appeared in dir() and help() output on the primary class (the one
containing the partialmethod objects). Suppose I have
class Something:
def meth(self, arg1, arg2):
"meth doc"
return arg1 + arg2
then in the metaclass for another class I construct an attribute (call it
"mymeth") which is a partialmethod object. When I (for example), run pydoc,
that other class's attribute appears as:
mymeth = <functools.partial object>
It would be nice if it at least included the doc string from meth, something
like:
mymeth = <functools.partial object>
meth doc
Even better would be a proper signature:
mymeth(self, arg1, arg2)
meth doc
In my copy of functools.partialmethod, I inserted an extra line in __get__,
right after the call to partial():
results.__doc__ = self.func.__doc__
That helps a bit, as I can
print("mymeth doc:", inst.mymeth.__doc__)
and see
mymeth doc: meth doc
displayed. That's not enough for help()/pydoc though.
I suspect the heavy lifting will have to be done in pydoc.Doc.document().
inspect.isroutine() returns False for functools.partial objects. I also see
_signature_get_partial() in inspect.py. That might be the source of the
problem. When I create a partialmethod object in my little example, it actually
looks like a functools.partial object, not a partialmethod object. It's not
clear that this test:
if isinstance(partialmethod, functools.partialmethod):
in inspect._signature_from_callable() is testing for the correct type.
Apologies that I can't easily provide a detailed example. My Python 2.x
metaclass example (where I'm smashing methods from one class into another)
doesn't work in Python 3.x for some reason, the whole partialmethod thing isn't
available in Python 2.x (inspect doesn't know about partialmethod or partial)
and it's not really a "hello world"-sized example anyway. I'll beat on things a
bit more to try and craft a workable Python 3.x example.
----------
components: Library (Lib)
messages: 292050
nosy: skip.montanaro
priority: normal
severity: normal
status: open
title: functools.partialmethod should look more like what it's impersonating.
type: enhancement
versions: Python 3.7
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue30129>
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