[Python-ideas] Dynamic getting of __doc__ of a function

Marko Ristin-Kaufmann marko.ristin at gmail.com
Sun Oct 7 12:17:47 EDT 2018

@Jonathan: thanks! I'll have a look at your links.

So there are actually two issues if I understand correctly:
* help() ignoring the property getter when invoked on an instance
* built-in class function ignoring the property getter (some_func.__doc__
set to a property returns the property instead of invoking the getter)

Is the second issue also problematic or the built-ins are meant to ignore
properties and there should be no fix? I think I'm misunderstanding
something here.


Le dim. 7 oct. 2018 à 17:37, Jonathan Fine <jfine2358 at gmail.com> a écrit :

> Hi Marko
> You wrote:
> > I just couldn't figure out how to make the __doc__ attribute of a
> function a getter. Is this a bug or am I making a mistake? If it's my
> mistake, is there any other way how to dynamically __doc__ a function or am
> I forced to set __doc__ of a function at the decoration time?
> Thank you for your clear examples. I'm not sure, but I may have found
> the problem.
> As I recall, setting obj.attr to a property won't work. Instead, you
> have to set type(obj).attr to the property. And now you come up
> against a problem. You can't set __doc__ on the type 'function', nor
> can you subclass the type 'function'.
> >>> def fn(): pass
> >>> type(fn)
> <class 'function'>
> >>> type(fn).__doc__
> 'function(code, globals[, name[, argdefs[, closure]]]) [snip]'
> >>> type(fn).__doc__ = None
> TypeError: can't set attributes of built-in/extension type 'function'
> >>> class FN(type(fn)): pass
> TypeError: type 'function' is not an acceptable base type
> As I (more vaguely) recall, something was done recently to add a get
> attribute property that works directly on objects, rather than on
> instances of a class. But I've not been able to find it. Perhaps I
> misunderstood PEP 562.
> Some perhaps relevant URLs:
> https://www.python.org/dev/peps/pep-0224/ Attribute Docstrings
> https://www.python.org/dev/peps/pep-0549/ Instance Descriptors
> https://www.python.org/dev/peps/pep-0562/ Module __getattr__ and __dir__
> https://stackoverflow.com/questions/2447353/getattr-on-a-module
> --
> Jonathan
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