python / python/mypy

`dataclass` is not `Hashable`

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#11,463 5 comments 1 reaction 0 assignees View on GitHub

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bug topic-dataclasses
Dominant language
Python
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Description

from dataclasses import dataclass
from typing import Hashable


@dataclass
class SusDataclass:
    b = "AMONGUS"


h: Hashable = SusDataclass()  # SUS ALERT!

d = {
    SusDataclass(): 1  # SUS ALERT! fails at runtime
}

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Research direction

No source file or test is named. Start by reproducing the shown dataclass and dictionary examples, then trace mypy's dataclass and Hashable handling. Done means the checker consistently reports the runtime-relevant hashability of this case, with regression coverage for the example.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
devtools
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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