assertion failure in ctypes in case an _anonymous_ attr appears outside _fields_

[orenmn]

BPO	31490
Nosy	@serhiy-storchaka, @orenmn
PRs	bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_ #3615 [3.6] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) #3774 [2.7] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) #3780 [2.7] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) #3952

^{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 2017-10-12.15:02:42.915>
created_at = <Date 2017-09-16.09:57:38.930>
labels = ['ctypes', '3.7', 'type-crash']
title = 'assertion failure in ctypes in case an _anonymous_ attr appears outside _fields_'
updated_at = <Date 2017-10-12.15:02:42.914>
user = 'https://github.com/orenmn'

bugs.python.org fields:

activity = <Date 2017-10-12.15:02:42.914>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2017-10-12.15:02:42.915>
closer = 'serhiy.storchaka'
components = ['ctypes']
creation = <Date 2017-09-16.09:57:38.930>
creator = 'Oren Milman'
dependencies = []
files = []
hgrepos = []
issue_num = 31490
keywords = ['patch']
message_count = 6.0
messages = ['302331', '302363', '303091', '303108', '303908', '304243']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'Oren Milman']
pr_nums = ['3615', '3774', '3780', '3952']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue31490'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7']

[orenmn]

The following code causes an assertion failure:
import ctypes
class BadStruct(ctypes.Structure):
_fields_ = []
_anonymous_ = ['foo']
foo = None

this is because MakeAnonFields() (in Modules/_ctypes/stgdict.c) goes over the
names specified in _anonymous_, and looks each name up in the class by calling
PyObject_GetAttr().
in case an attribute of such a name is found (i.e. PyObject_GetAttr() succeeded),
MakeAnonFields() assumes that the attribute was created by MakeFields(), so it
asserts the type of the attribute is PyCField_Type.

however, PyObject_GetAttr() would succeed also in case it is a normal attribute
specified by the user, but isn't specified in _fields_, as in the code above.
in such a case, the type of the attribute is not PyCField_Type, and so the
assertion fails.

[serhiy-storchaka]

New changeset 30b61b5 by Serhiy Storchaka (Oren Milman) in branch 'master':
bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (bpo-3615)
30b61b5

[serhiy-storchaka]

New changeset bdb215b by Serhiy Storchaka (Miss Islington (bot)) in branch '3.6':
[3.6] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) (bpo-3774)
bdb215b

[serhiy-storchaka]

New changeset 9bfa55b by Serhiy Storchaka (Miss Islington (bot)) in branch '2.7':
[2.7] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) (bpo-3780)
9bfa55b

[serhiy-storchaka]

In 2.7 "%U" is not recognized in the format string.

>>> class Name(Structure):
...     _fields_ = []
...     _anonymous_ = ["x"]
...     x = 42
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: '%U' is specified in _anonymous_ but not in _fields_

[serhiy-storchaka]

New changeset fb3bb8d by Serhiy Storchaka (Oren Milman) in branch '2.7':
[2.7] bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (GH-3615) (bpo-3952)
fb3bb8d