[New-bugs-announce] [issue45531] field "mro" behaves strangely in dataclass

[Finite State Machine]

New submission from Finite State Machine <python at state-machine.ca>:

The following Python script:

    from dataclasses import dataclass

    @dataclass
    class A:
        mro: object
        x: object

Results in the following unexpected exception:

    Traceback (most recent call last):
      File "/Users/dsuffling/.pyenv/versions/3.10.0/lib/python3.10/runpy.py", line 196, in _run_module_as_main
        return _run_code(code, main_globals, None,
      File "/Users/dsuffling/.pyenv/versions/3.10.0/lib/python3.10/runpy.py", line 86, in _run_code
        exec(code, run_globals)
      File "/Users/dsuffling/names/junk.py", line 6, in <module>
        class A:
      File "/Users/dsuffling/.pyenv/versions/3.10.0/lib/python3.10/dataclasses.py", line 1178, in dataclass
        return wrap(cls)
      File "/Users/dsuffling/.pyenv/versions/3.10.0/lib/python3.10/dataclasses.py", line 1169, in wrap
        return _process_class(cls, init, repr, eq, order, unsafe_hash,
      File "/Users/dsuffling/.pyenv/versions/3.10.0/lib/python3.10/dataclasses.py", line 1019, in _process_class
        _init_fn(all_init_fields,
      File "/Users/dsuffling/.pyenv/versions/3.10.0/lib/python3.10/dataclasses.py", line 540, in _init_fn
        raise TypeError(f'non-default argument {f.name!r} '
    TypeError: non-default argument 'x' follows default argument


The name of the first attribute ('mro') is critical; without it the problem does not occur.

It appears that 'mro' is somehow interacting with the 'mro' attribute of the 'type' object.

This issue has been verified to occur with CPython 3.10.0.

----------
components: Library (Lib)
messages: 404378
nosy: finite-state-machine
priority: normal
severity: normal
status: open
title: field "mro" behaves strangely in dataclass
type: behavior
versions: Python 3.10

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45531>
_______________________________________