[Python-Dev] Quick poll: should help() show bound arguments? (original) (raw)

Steven D'Aprano steve at pearwood.info
Sat Jan 25 05:36:49 CET 2014

On Fri, Jan 24, 2014 at 08:07:43PM -0800, Larry Hastings wrote:

(Quick, because apparently nobody reads the long ones!) In Python 3.3: >>> class C: ... def foo(self, a): pass ... >>> c = C() >>> help(c.foo) shows you the signature "foo(self, a)".

That matches the function declaration as defined right there in the class.

As in, it claims it accepts two parameters. The function actually only accepts one parameter, because "self" has already been bound.

No, that's wrong. The function C.foo accepts two parameters, self and a, exactly as declared. The method c.foo accepts only one.

inspect.signature gets this right:

>>> import inspect >>> str(inspect.signature(c.foo)) '(a)' but inspect.getfullargspec does not: >>> inspect.getfullargspec(c.foo) FullArgSpec(args=['self', 'a'], varargs=None, varkw=None, defaults=None, kwonlyargs=[], kwonlydefaults=None, annotations={})

That's arguable. Should inspect give the argument spec of the method object or the function object? I can see arguments for both. Backwards-compatibility argues against changing either, though.

help() is another story. Since help() is documentation aimed at the end-user, we can change it without worrying about backward compatibility. Ideally, help() ought to distingush between the two cases. I see that it already does, but not very well.

help(c.foo) in Python 3.3 gives:

Help on method foo in module __main__:

foo(self, a) method of __main__.C instance

while help(C.foo) gives:

Help on function foo in module __main__:

foo(self, a)

I think in the bound method case, it should drop the "self":

Help on method foo in module __main__:

foo(a) method of __main__.C instance

and in the function (previously: unbound method) case, it should show the "self" and the class:

Help on function foo in module __main__:

foo(self, a) method of class __main__.C

although I'm not sure how that second one is possible, now that unbound methods are gone and C.foo returns a plain function.

(Hmmm, perhaps getting rid of unbound methods was a mistake...)

A) pydoc and help() should not show bound parameters in the signature, like inspect.signature. B) pydoc and help() should show bound parameters in the signature, like inspect.getfullargspec.

Provided they are described as methods rather than functions, bound methods should not show self. Likewise for classmethod and cls. That is, I'm voting +1 on A provided help() doesn't confuse methods and functions.

-- Steven

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