[Debian-science-sagemath] python2.7: Fix for #5322 breaks SageMath

[Tobias Hansen]

Source: python2.7
Severity: important
Version: 2.7.13~rc1-1
Control: forwarded -1 https://bugs.python.org/issue5322#msg282852

Dear maintainer,

the fix for Python issue #5322 that was included in Python 2.7.13rc1
breaks backwards compatibility [1]. Another Python change that broke
backwards compatibility in the same way was reverted for that reason a
while ago [2], so I hope this change will also eventually be reverted or
changed upstream.

The problem is, this breaks SageMath, which we wanted to upload to NEW
this weekend in order to have it included in Stretch. We are also trying
to find a workaround on the Sage side in [3], but this seems to be very
complicated. SageMath uses inheritance with cdef classes hundreds of
times, and all these cases would need to be fixed to pass the new
stricter check of Python.

Can we revert this change in the next few days please? I will attach a
patch to this bug report later today.

Best,
Tobias

[1] https://bugs.python.org/issue5322#msg282852
[2] https://bugs.python.org/issue25731#msg262922
[3] https://trac.sagemath.org/ticket/22037