Broken help() on metaclasses

[serhiy-storchaka]

BPO	35614
Nosy	@ncoghlan, @abalkin, @merwok, @serhiy-storchaka, @CuriousLearner
PRs	bpo-35614: Fix pydoc help() on metaclasses #11357 bpo-35614: Fix pydoc help() on metaclasses #11357 bpo-35614: Fix pydoc help() on metaclasses #11357

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-12-31.05:19:43.925>
created_at = <Date 2018-12-29.15:21:50.099>
labels = ['3.8', 'type-bug', 'library']
title = 'Broken help() on metaclasses'
updated_at = <Date 2018-12-31.05:19:43.924>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2018-12-31.05:19:43.924>
actor = 'ncoghlan'
assignee = 'none'
closed = True
closed_date = <Date 2018-12-31.05:19:43.925>
closer = 'ncoghlan'
components = ['Library (Lib)']
creation = <Date 2018-12-29.15:21:50.099>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 35614
keywords = ['patch', 'patch', 'patch']
message_count = 4.0
messages = ['332720', '332726', '332727', '332802']
nosy_count = 5.0
nosy_names = ['ncoghlan', 'belopolsky', 'eric.araujo', 'serhiy.storchaka', 'CuriousLearner']
pr_nums = ['11357', '11357', '11357']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue35614'
versions = ['Python 3.8']

[serhiy-storchaka]

$ ./python -m pydoc abc
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2765, in <module>
    cli()
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2727, in cli
    help.help(arg)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1967, in help
    elif request: doc(request, 'Help on %s:', output=self._output)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1690, in doc
    pager(render_doc(thing, title, forceload))
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1683, in render_doc
    return title % desc + '\n\n' + renderer.document(object, name)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 385, in document
    if inspect.ismodule(object): return self.docmodule(*args)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1182, in docmodule
    contents.append(self.document(value, key, name))
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 386, in document
    if inspect.isclass(object): return self.docclass(*args)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1258, in docclass
    (str(cls.__name__) for cls in object.__subclasses__()
TypeError: descriptor '__subclasses__' of 'type' object needs an argument

$ ./python -m pydoc enum
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2765, in <module>
    cli()
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2727, in cli
    help.help(arg)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1967, in help
    elif request: doc(request, 'Help on %s:', output=self._output)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1690, in doc
    pager(render_doc(thing, title, forceload))
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1683, in render_doc
    return title % desc + '\n\n' + renderer.document(object, name)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 385, in document
    if inspect.ismodule(object): return self.docmodule(*args)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1182, in docmodule
    contents.append(self.document(value, key, name))
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 386, in document
    if inspect.isclass(object): return self.docclass(*args)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1258, in docclass
    (str(cls.__name__) for cls in object.__subclasses__()
TypeError: descriptor '__subclasses__' of 'type' object needs an argument

"object" is a metaclass (abc.ABCMeta or enum.EnumMeta) in tracebacks above.

The regression was introduced in bpo-8525.

[serhiy-storchaka]

It fails also for builtin "type".

$ ./python -m pydoc type
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/home/serhiy/py/cpython/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2765, in <module>
    cli()
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 2727, in cli
    help.help(arg)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1967, in help
    elif request: doc(request, 'Help on %s:', output=self._output)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1690, in doc
    pager(render_doc(thing, title, forceload))
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1683, in render_doc
    return title % desc + '\n\n' + renderer.document(object, name)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 386, in document
    if inspect.isclass(object): return self.docclass(*args)
  File "/home/serhiy/py/cpython/Lib/pydoc.py", line 1258, in docclass
    (str(cls.__name__) for cls in object.__subclasses__()
TypeError: descriptor '__subclasses__' of 'type' object needs an argument

[serhiy-storchaka]

There are two ways of solving this issue: 1) skip this chunk of code if object is a type subclass, 2) use type.__subclasses__(object) instead of object.__subclasses__().

[ncoghlan]

New changeset b539cef by Nick Coghlan (Sanyam Khurana) in branch 'master':
bpo-35614: Fix pydoc help() on metaclasses (bpo-11357)
b539cef