inspect() changes in Python3.4 are not compatible with objects that implement special __bool__, __eq__

[zzzeek]

BPO	23898
Nosy	@bitdancer, @1st1
Files	issue23898.patch

^{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 = 'https://github.com/1st1'
closed_at = <Date 2015-05-21.19:47:07.370>
created_at = <Date 2015-04-09.14:34:46.137>
labels = ['library']
title = 'inspect() changes in Python3.4 are not compatible with objects that implement special __bool__, __eq__'
updated_at = <Date 2015-05-21.20:05:39.452>
user = 'https://bugs.python.org/zzzeek'

bugs.python.org fields:

activity = <Date 2015-05-21.20:05:39.452>
actor = 'zzzeek'
assignee = 'yselivanov'
closed = True
closed_date = <Date 2015-05-21.19:47:07.370>
closer = 'yselivanov'
components = ['Library (Lib)']
creation = <Date 2015-04-09.14:34:46.137>
creator = 'zzzeek'
dependencies = []
files = ['38882']
hgrepos = []
issue_num = 23898
keywords = ['patch']
message_count = 12.0
messages = ['240331', '240335', '240337', '240344', '240370', '240373', '240374', '240400', '241100', '243783', '243784', '243785']
nosy_count = 4.0
nosy_names = ['r.david.murray', 'zzzeek', 'python-dev', 'yselivanov']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue23898'
versions = ['Python 3.4', 'Python 3.5']

[zzzeek]

this bug appeared in Python 3.4. The inspect.classify_class_attrs compares the identity objects of unknown type using the == operator unnecessarily and also evaluates objects of unknown type assuming they return True for a straight boolean evaluation. This breaks among other things the ability to use the help() function with SQLAlchemy mapped objects.

Demo:

class MySpecialObject(object):

    def __eq__(self, other):
        return MySpecialObject()

    def __bool__(self):
        raise NotImplementedError(
            "This object does not specify a boolean value")


class MyClass(object):
    some_thing = MySpecialObject()

import inspect

print(inspect.classify_class_attrs(MyClass))

# ultimate goal: help(MyClass)

A patch here would be to compare unknown objects for identity using the is operator as well as using is not None when asserting that an object of unknown type is non-None. This patch resolves:

--- inspect_orig.py	2015-04-09 10:28:46.000000000 -0400
+++ inspect.py	2015-04-09 10:29:37.000000000 -0400
@@ -380,7 +380,7 @@
                     # first look in the classes
                     for srch_cls in class_bases:
                         srch_obj = getattr(srch_cls, name, None)
-                        if srch_obj == get_obj:
+                        if srch_obj is get_obj:
                             last_cls = srch_cls
                     # then check the metaclasses
                     for srch_cls in metamro:
@@ -388,7 +388,7 @@
                             srch_obj = srch_cls.__getattr__(cls, name)
                         except AttributeError:
                             continue
-                        if srch_obj == get_obj:
+                        if srch_obj is get_obj:
                             last_cls = srch_cls
                     if last_cls is not None:
                         homecls = last_cls
@@ -402,7 +402,7 @@
             # unable to locate the attribute anywhere, most likely due to
             # buggy custom __dir__; discard and move on
             continue
-        obj = get_obj or dict_obj
+        obj = get_obj if get_obj is not None else dict_obj
         # Classify the object or its descriptor.
         if isinstance(dict_obj, staticmethod):
             kind = "static method"

[bitdancer]

This looks reasonable to me. It would be great if the patch could be attached to the issue as a patch file, including some tests.

[zzzeek]

It would be great if the patch could be attached to the issue as a patch file, including some tests.

the mantra we all share. I'll take a look.

[zzzeek]

patch w/ test

[1st1]

The patch looks good, Mike. Could you please sign PSF Contributor Agreement?

[zzzeek]

hi Yury -

I did sign it earlier today. It should have been sent off to the person that manages that, at least that's what the email receipt said.

[1st1]

Mike, please ping me when they process it. I'll commit your patch.

[zzzeek]

hi Yury -

I have a confirmation including a PDF attachment of the agreement, the message reads:

" Python Contributor Agreement Form between Python Software Foundation and Michael Bayer is Signed and Filed!

From: Ewa Jodlowska (Python Software Foundation)
To: Ewa Jodlowska and Michael Bayer "

can I forward that to you?

[zzzeek]

my star went through.

let's merge.

[python-dev]

New changeset fb9addfdfc35 by Yury Selivanov in branch '3.4':
bpo-23898: Fix inspect.classify_class_attrs() to work with __eq__
https://hg.python.org/cpython/rev/fb9addfdfc35

New changeset d6a9d225413a by Yury Selivanov in branch 'default':
bpo-23898: Fix inspect.classify_class_attrs() to work with __eq__
https://hg.python.org/cpython/rev/d6a9d225413a

[1st1]

Merged. Thanks for the bug report and patch, Mike!

[zzzeek]

thanks for the merge!