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Message from discussion Override a method but inherit the docstring
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Rhodri James  
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 More options Jul 16 2009, 9:31 pm
Newsgroups: comp.lang.python
From: "Rhodri James" <rho...@wildebst.demon.co.uk>
Date: Fri, 17 Jul 2009 02:31:43 +0100
Local: Thurs, Jul 16 2009 9:31 pm
Subject: Re: Override a method but inherit the docstring
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On Fri, 17 Jul 2009 02:01:49 +0100, Ben Finney  

<ben+pyt...@benfinney.id.au> wrote:
> Howdy all,

> The following is a common idiom::

>     class FooGonk(object):
>         def frobnicate(self):
>             """ Frobnicate this gonk. """
>             basic_implementation(self.wobble)

>     class BarGonk(FooGonk):
>         def frobnicate(self):
>             special_implementation(self.warble)

> The docstring for ‘FooGonk.frobnicate’ is, intentionally, perfectly
> applicable to the ‘BarGonk.frobnicate’ method also. Yet in overriding
> the method, the original docstring is not associated with it.

> Ideally there would be a way to specify that the docstring should be
> inherited. The best I can come up with is::

>     class BarGonk(FooGonk):
>         def frobnicate(self):
>             special_implementation(self.warble)
>         frobnicate.__doc__ = FooGonk.frobnicate.__doc__

> but that violates DRY (the association between BarGonk and FooGonk is
> being repeated),

Not really.  Consider the case of BarGonk being a subclass of FooGonk
and BazGonk; which docstring would you wish to inherit?

> puts the docstring assignment awkwardly after the end
> of the method instead of at the beginning where docstrings normally go,
> and reads poorly besides.

Sounds like a job for a decorator!

(This is probably unbelievably ugly and unwise, since I don't use
decorators at all often.)

def copydoc(cls):
     def _fn(fn):
         if fn.__name__ in cls.__dict__:
             fn.__doc__ = cls.__dict__[fn.__name__].__doc__
         return fn
     return _fn

class BarGonk(FooGonk):
     @copydoc(FooGonk)
     def frobnicate(self):
         special_implementation(self.warble)

--
Rhodri James *-* Wildebeest Herder to the Masses


 
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