[New-bugs-announce] [issue39247] dataclass defaults and property don't work together

[Michael Robellard]

New submission from Michael Robellard <mike at robellard.com>:

I ran into a strange issue while trying to use a dataclass together with a property.

I have it down to a minumum to reproduce it:

import dataclasses

@dataclasses.dataclass
class FileObject:
    _uploaded_by: str = dataclasses.field(default=None, init=False)
    uploaded_by: str = None

    def save(self):
        print(self.uploaded_by)

    @property
    def uploaded_by(self):
        return self._uploaded_by

    @uploaded_by.setter
    def uploaded_by(self, uploaded_by):
        print('Setter Called with Value ', uploaded_by)
        self._uploaded_by = uploaded_by

p = FileObject()
p.save()
This outputs:

Setter Called with Value  <property object at 0x7faeb00150b0>
<property object at 0x7faeb00150b0>
I would expect to get None instead

Here is the StackOverflow Question where I started this:
https://stackoverflow.com/questions/59623952/weird-issue-when-using-dataclass-and-property-together

----------
components: Library (Lib)
messages: 359528
nosy: Michael Robellard
priority: normal
severity: normal
status: open
title: dataclass defaults and property don't work together
type: behavior
versions: Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39247>
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