$ ./python -m pydoc socket.AddressFamily
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 171, in _run_module_as_main
    "__main__", mod_spec)
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2600, in <module>
    cli()
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2565, in cli
    help.help(arg)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1847, in help
    elif request: doc(request, 'Help on %s:', output=self._output)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1585, in doc
    pager(render_doc(thing, title, forceload))
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1578, in render_doc
    return title % desc + '\n\n' + renderer.document(object, name)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 357, in document
    if inspect.isclass(object): return self.docclass(*args)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1284, in docclass
    lambda t: t[1] == 'data')
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1248, in spilldata
    getattr(object, name, None) or homecls.__dict__[name],
KeyError: 'AF_UNSPEC'

But it works with other enum types: socket.SocketType, plistlib.PlistFormat, ssl.Purpose.

This is the preliminary patch for this bug.

The bug happens because AddressFamily.AF_UNSPEC is 0. Then you have this if condition:
getattr(object, name, None) or homecls.__dict__[name]

I'll contemplate whether we should add unit test for this or not.

I just realized that Enum member could be None. I'll think how to improve this patch.

Just use getattr() without third argument and catch AttributeError.

Here is the second preliminary patch. I'll think about the way to avoid dependency to socket module.

Here is the second patch, avoiding dependency to socket.AddressFamily (though it adds dependency to enum library) in test.

The fix itself looks good, but the test can be better. You write temporary file in current directory. this can fail for different reasons, Python can crash and left undeleted file, this file can overwrite existing file. The render_doc() function is last module level function in a traceback, and it can be used for testing, temporary file will be not needed.

Interesting, that the documentation for AddressFamily (unlike to SocketType) isn't generated in html doc. May be this is unrelated issue, but if this is related, it would be good to fix it too. Otherwise it needs separate issue.

Thanks for the review, Serhiy! Here is the patch addressing Serhiy's concern.

New changeset 8a3e896f0681 by Serhiy Storchaka in branch 'default':
Issue #20654: Fixed pydoc for enums with zero value.  Patch by Vajrasky Kok.
http://hg.python.org/cpython/rev/8a3e896f0681

Thank you Vajrasky!