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

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.

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

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

New changeset d896985bb2de49046f9b6879e906d1e4db255e23 by Serhiy Storchaka in branch 'master':
bpo-25794: Fix `type.__setattr__()` for non-interned attribute names. (#1652)
https://github.com/python/cpython/commit/d896985bb2de49046f9b6879e906d1e4db255e23

New changeset e9f9b042781e3cb480315860bcdf7b7d22cba0f8 by Serhiy Storchaka in branch '2.7':
[2.7] bpo-25794: Fix `type.__setattr__()` for non-interned or unicode attribute names. (GH-1652) (#1675)
https://github.com/python/cpython/commit/e9f9b042781e3cb480315860bcdf7b7d22cba0f8

New changeset 193f7e094f070cecbc6faea6dffafb80ea9e7536 by Serhiy Storchaka in branch '3.6':
[3.6] bpo-25794: Fix `type.__setattr__()` for non-interned attribute names. (GH-1652) (#1673)
https://github.com/python/cpython/commit/193f7e094f070cecbc6faea6dffafb80ea9e7536

New changeset 4a86fe9d3f5e7af6f019ae22536eec228f04e22e by Serhiy Storchaka in branch '3.5':
[3.5] bpo-25794: Fix `type.__setattr__()` for non-interned attribute names. (GH-1652) (#1674)
https://github.com/python/cpython/commit/4a86fe9d3f5e7af6f019ae22536eec228f04e22e