Metaclass to rewrite class __doc__?

[Skip Montanaro]

I stumbled upon this use of a metaclass to modify function docstrings:

http://www.jesshamrick.com/2013/04/17/rewriting-python-docstrings-with-a-metaclass/

In certain circumstances (mostly when extending some Pybind11 wrappers), it
might be nice to extend/modify a class's docstring in a similar manner.
Alas, my first attempt at that was unsuccessful. All I was trying to do was
the following (skipping any error checking):

class _RewriteDocMeta(type):
    def __new__(cls, name, parents, attrs):
        cls.__doc__ = parents[0].__doc__ + "\n\n" + cls.__doc__
        return super(_RewriteDocMeta, cls).__new__(cls, name, parents,
attrs)

Using that as the __metaclass__ for a class resulted in:

    ... '__doc__' of 'type' objects is not writable.

Does this imply a requirement for a metaclass metaclass? In Jess Hamrick's
blog, she built entirely new function objects out of their constituent
bits, then set their __doc__ attributes. She didn't attempt to
replace/modify an existing function (or unbound method) docstring. I fear
that might be required in this case as well.

This works:

class F(object):
  "F doc"
  pass

G = type(F)("G", (F,), {"__doc__": F.__doc__ + "\n" + "G doc"})

but I'm not sure how to translate that into a working __metaclass__ example
(my brain is slowly exploding
<https://www.python.org/doc/essays/metaclasses/>[*] as I write this)...

Thx,

Skip

[*] Whatever happened to Don Beaudry?