Inherit docstrings in Python class inheritance

Question

I'm trying to do some class inheritance in Python. I'd like each class and inherited class to have good docstrings. So I think for the inherited class, I'd like it to:

• inherit the base class docstring
• maybe append relevant extra documentation to the docstring

Is there any (possibly elegant or pythonic) way of doing this sort of docstring manipulation in a class inheritance situation? How about for multiple inheritance?

Answer 1

You're not the only one! There was a discussion on comp.lang.python about this a while ago, and a recipe was created. Check it out here.

"""
doc_inherit decorator

Usage:

class Foo(object):
    def foo(self):
        "Frobber"
        pass

class Bar(Foo):
    @doc_inherit
    def foo(self):
        pass 

Now, Bar.foo.__doc__ == Bar().foo.__doc__ == Foo.foo.__doc__ == "Frobber"
"""

from functools import wraps

class DocInherit(object):
    """
    Docstring inheriting method descriptor

    The class itself is also used as a decorator
    """

    def __init__(self, mthd):
        self.mthd = mthd
        self.name = mthd.__name__

    def __get__(self, obj, cls):
        if obj:
            return self.get_with_inst(obj, cls)
        else:
            return self.get_no_inst(cls)

    def get_with_inst(self, obj, cls):

        overridden = getattr(super(cls, obj), self.name, None)

        @wraps(self.mthd, assigned=('__name__','__module__'))
        def f(*args, **kwargs):
            return self.mthd(obj, *args, **kwargs)

        return self.use_parent_doc(f, overridden)

    def get_no_inst(self, cls):

        for parent in cls.__mro__[1:]:
            overridden = getattr(parent, self.name, None)
            if overridden: break

        @wraps(self.mthd, assigned=('__name__','__module__'))
        def f(*args, **kwargs):
            return self.mthd(*args, **kwargs)

        return self.use_parent_doc(f, overridden)

    def use_parent_doc(self, func, source):
        if source is None:
            raise NameError, ("Can't find '%s' in parents"%self.name)
        func.__doc__ = source.__doc__
        return func

doc_inherit = DocInherit