[New-bugs-announce] [issue33268] iteration over attrs in metaclass' __new__ affects class' __name__

[tkhyn]

New submission from tkhyn <thomas.khyn_python at m4x.org>:

The following script, run with python 3.6.5, highlights an issue with the class' __name__ attribute being set incorrectly just because of a loop in the metaclass' __new__ method:

class MC(type):
    def __new__(mcs, name, bases, attrs):
        for name, attr in attrs.items():
            pass
        return super(MC, mcs).__new__(mcs, name, bases, attrs)

class C(metaclass=MC):
    a = None

print(C.__name__)


Expected output: "C"
Actual output: "a"

Comment the for loop and you get the expected output!

On Python 2.7.13, the amended code exposes the same bug:

class MC(type):
    def __new__(mcs, name, bases, attrs):
        for name, attr in attrs.items():
            pass
        return super(MC, mcs).__new__(mcs, name, bases, attrs)

class C(object):
    __metaclass__ = MC
    a = None

print C.__name__

output is "__metaclass__" and should be "C"

----------
components: Interpreter Core
messages: 315218
nosy: tkhyn
priority: normal
severity: normal
status: open
title: iteration over attrs in metaclass' __new__ affects class' __name__
versions: Python 2.7, Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33268>
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