duplicate docstrings

[Felix Wiemann]

Steven Bethard wrote:

> class C(object):
>      def foo(self):
>          """Foo things"""
>          ...
>
> class D(object):
>      def foo(self):
>          """Foo things"""
>          ...
>
> It bothers me that I'm basically writing the same docstrings multiple
> times.  I guess what I really want to do is just write the docstrings
> for the interface I'm describing, and only supply docstrings in the
> classes when they need to differ from the interface docstrings.
>
> Is there a good way to do this?  If it's necessary, I can have C and D
> inherit from another class...

Use a common interface type and a metaclass which copies method
docstrings from base classes:

------------------------------------------------------------------------------
#!/usr/bin/env python

import inspect


class DocstringMetaclass(type):
    
    """Copy method docstrings."""
    
    def __init__(cls, *args):
        super(DocstringMetaclass, cls).__init__(*args)
        for name, method in cls.__dict__.iteritems():
            # method is a function, not a method, so we use isfunction().
            if not inspect.isfunction(method) or method.__doc__ is not None:
                continue
            for c in cls.mro():
                if hasattr(c, name):
                    m = getattr(c, name)
                    if inspect.ismethod(m) and m.__doc__ is not None:
                        method.__doc__ = m.__doc__
                        break


class Interface(object):

    __metaclass__ = DocstringMetaclass

    def foo(self):
        """Foo things"""

    def bar(self):
        """Bar things"""

    def baz(self):
        """Baz things in a C manner"""


class Implementation(Interface):

    def foo(self):
        pass

    def bar(self):
        pass

    def baz(self):
        pass


print Implementation.foo.__doc__
print Implementation.bar.__doc__
print Implementation.baz.__doc__
------------------------------------------------------------------------------

Output:

Foo things
Bar things
Baz things in a C manner

-- 
Felix Wiemann -- http://www.ososo.de/