[New-bugs-announce] [issue33094] dataclasses: ClassVar attributes are not working properly

[Adrian Stachlewski]

New submission from Adrian Stachlewski <adrian.stachlewski at gmail.com>:

Class variables should behave in the same way whether with or without ClassVar annotation. Unfortunately there are not.

class A:
    __slots__ = ()
    x: ClassVar = set()

A()  # it's ok

@dataclass
class B:
    __slots__ = ()
    x = set()

B()  # ok too

@dataclass
class C:
    __slots__ = ()
    # cannot use set() because of error
    x: ClassVar = field(default_factory=set) 

C()  # AttributeError: 'C' object has no attribute 'x'

Exception is raised from __init__ method, with flag init=False nothing changes. 

Python version: 3.7.0b2

----------
components: Library (Lib)
messages: 314017
nosy: stachel
priority: normal
severity: normal
status: open
title: dataclasses: ClassVar attributes are not working properly
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33094>
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