[New-bugs-announce] [issue43176] Dataclasses derived from empty frozen bases skip immutability checks

[Iurii Kemaev]

New submission from Iurii Kemaev <y.kemaev at gmail.com>:

Dataclasses derived from empty frozen bases skip immutability checks.

Repro snippet:

```
import dataclasses

@dataclasses.dataclass(frozen=True)
class Base:
  pass

@dataclasses.dataclass
class Derived(Base):
  a: int

d = Derived(2)
# OK
```

Usecase: sometimes developers define an empty frozen base dataclass with detailed docs and require other dataclasses to inherit from it as a code contract to avoid accidental in-place modifications. 
This bug makes this strategy ineffective.

Affects all versions of Python that support dataclasses (including the backport for py3.6).

----------
components: Library (Lib)
messages: 386695
nosy: hbq1
priority: normal
pull_requests: 23278
severity: normal
status: open
title: Dataclasses derived from empty frozen bases skip immutability checks
type: behavior
versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue43176>
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