New submission from Glyph Lefkowitz <gl...@twistedmatrix.com>:
Consider the following example that attempts to make a series of types sortable
by their class name:
from functools import total_ordering
@total_ordering
class SortableMeta(type):
def __new__(cls, name, bases, ns):
return super().__new__(cls, name, bases, ns)
def __lt__(self, other):
if not isinstance(other, SortableMeta):
pass
return self.__name__ < other.__name__
def __eq__(self, other):
if not isinstance(other, SortableMeta):
pass
return self.__name__ == other.__name__
class B(metaclass=SortableMeta):
pass
class A(metaclass=SortableMeta):
pass
print(A < B)
print(A > B)
This should just print "True", "False", but instead the second comparison
raises this exception:
Traceback (most recent call last):
File "total_ordering_metaclass.py", line 27, in <module>
print(A > B)
File "lib/python3.9/functools.py", line 91, in _gt_from_lt
op_result = self.__lt__(other)
TypeError: expected 1 argument, got 0
The problem here is that functools considers .__special__ to be equivalent to
operator.special. I'm pretty sure this should be invoking "self < other"
rather than self.__lt__(other).
----------
components: Library (Lib)
messages: 397278
nosy: glyph
priority: normal
severity: normal
stage: needs patch
status: open
title: functools.total_ordering doesn't work with metaclasses
type: behavior
versions: Python 3.7, Python 3.8, Python 3.9
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue44605>
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