__setattr__ does not always overload operators

[DominikSchmid]

BPO	25794
Nosy	@berkerpeksag, @serhiy-storchaka, @eryksun, @mlouielu
PRs	bpo-25794: Fix type.__setattr__() for non-interned attribute names. #1652 [3.6] bpo-25794: Fix type.__setattr__() for non-interned attribute names. (GH-1652) #1673 [3.5] bpo-25794: Fix type.__setattr__() for non-interned attribute names. (GH-1652) #1674 [2.7] bpo-25794: Fix type.__setattr__() for non-interned or unicode attribute names. (GH-1652) #1675
Files	bug.py: source code reproducing the bug issue25794_2.patch

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

Show more details

GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2017-05-20.07:25:37.980>
created_at = <Date 2015-12-04.08:52:36.937>
labels = ['interpreter-core', 'type-bug', '3.7']
title = '__setattr__ does not always overload operators'
updated_at = <Date 2017-05-20.07:25:37.960>
user = 'https://bugs.python.org/DominikSchmid'

bugs.python.org fields:

activity = <Date 2017-05-20.07:25:37.960>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2017-05-20.07:25:37.980>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2015-12-04.08:52:36.937>
creator = 'Dominik Schmid'
dependencies = []
files = ['41234', '41236']
hgrepos = []
issue_num = 25794
keywords = ['patch']
message_count = 8.0
messages = ['255853', '255859', '255862', '292176', '294006', '294015', '294017', '294018']
nosy_count = 5.0
nosy_names = ['berker.peksag', 'serhiy.storchaka', 'eryksun', 'Dominik Schmid', 'louielu']
pr_nums = ['1652', '1673', '1674', '1675']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25794'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6', 'Python 3.7']

[DominikSchmid]

While implementing my own Integer class that keeps track of when operations are applied I noticed that setattr had a strange behaviour when I tried to wrap operator functions.

When the attribute string had a different id to its literal it failed to overload the operator.
Are we doing a 'is' rather than a '==' somewhere in setattr?

expected result:
139723705431168 a.__add__(b)= (5) a+b= (5)
139723705431168 a.__add__(b)= (5) a+b= (5)
139723704361584 a.__add__(b)= (5) a+b= (5)

actual result:
139723705431168    a.__add__(b)= (5)    a+b= (5)
139723705431168    a.__add__(b)= (5)    a+b= (5)
139723704361584    a.__add__(b)= (5)    a+b=
Traceback (most recent call last):
  File "/home/dom/Documents/leastOps/bug.py", line 41, in <module>
    testSetattr(funcName3)
  File "/home/dom/Documents/leastOps/bug.py", line 28, in testSetattr
    print '   a+b=', a+b
TypeError: unsupported operand type(s) for +: 'Integer' and 'Integer'

version:
2.7.10 (default, Oct 14 2015, 16:09:02)
[GCC 5.2.1 20151010]
ubuntu 14.10

[eryksun]

Normally Python code calls built-in setattr, which calls the C API PyObject_SetAttr. This API interns the attribute name before calling the type's tp_setattro or tp_setattr function. Interning the string is a critical step, since the implementation for updating slots assumes the name is interned.

The __setattr__ slot wrapper calls wrap_setattr in Objects/typeobject.c. In line with how PyObject_SetAttr works, the attached patch interns the name in wrap_setattr before calling the wrapped setattrofunc. For good measure it also applies the same change to wrap_delattr, though that's not strictly necessary.

[eryksun]

This updated patch calls PyUnicode_Check to ensure the name is a string before calling PyUnicode_InternInPlace.

[serhiy-storchaka]

Eryk, could you create a pull request? Please take into account my and Berker's comments on Rietveld.

[serhiy-storchaka]

New changeset d896985 by Serhiy Storchaka in branch 'master':
bpo-25794: Fix type.__setattr__() for non-interned attribute names. (bpo-1652)
d896985

[serhiy-storchaka]

New changeset e9f9b04 by Serhiy Storchaka in branch '2.7':
[2.7] bpo-25794: Fix type.__setattr__() for non-interned or unicode attribute names. (GH-1652) (bpo-1675)
e9f9b04

[serhiy-storchaka]

New changeset 193f7e0 by Serhiy Storchaka in branch '3.6':
[3.6] bpo-25794: Fix type.__setattr__() for non-interned attribute names. (GH-1652) (bpo-1673)
193f7e0

[serhiy-storchaka]

New changeset 4a86fe9 by Serhiy Storchaka in branch '3.5':
[3.5] bpo-25794: Fix type.__setattr__() for non-interned attribute names. (GH-1652) (bpo-1674)
4a86fe9