[New-bugs-announce] [issue44414] from __future__ import annotations breaks profiler's handling of dataclasses

[James Wilcox]

New submission from James Wilcox <wilcoxjay at gmail.com>:

This program behaves differently when run under the profiler (either profile or cProfile) versus when run normally.

```
from __future__ import annotations  # ***
import dataclasses

@dataclasses.dataclass
class C:
    x: dataclasses.InitVar[int]

    def __post_init__(self, x):
        print(f'hello {x}')

C(0)
```

Save this as foo.py. Then

    python foo.py

prints

    hello 0

but

    python -m profile foo.py

results in the traceback

```
Traceback (most recent call last):
  File "/Users/jrw12/.pyenv/versions/3.9.5/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Users/jrw12/.pyenv/versions/3.9.5/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/jrw12/.pyenv/versions/3.9.5/lib/python3.9/profile.py", line 610, in <module>
    main()
  File "/Users/jrw12/.pyenv/versions/3.9.5/lib/python3.9/profile.py", line 599, in main
    runctx(code, globs, None, options.outfile, options.sort)
  File "/Users/jrw12/.pyenv/versions/3.9.5/lib/python3.9/profile.py", line 99, in runctx
    return _Utils(Profile).runctx(statement, globals, locals, filename, sort)
  File "/Users/jrw12/.pyenv/versions/3.9.5/lib/python3.9/profile.py", line 62, in runctx
    prof.runctx(statement, globals, locals)
  File "/Users/jrw12/.pyenv/versions/3.9.5/lib/python3.9/profile.py", line 422, in runctx
    exec(cmd, globals, locals)
  File "foo.py", line 11, in <module>
    C(0)
  File "<string>", line 4, in __init__
TypeError: __post_init__() missing 1 required positional argument: 'x'
```

A similar traceback occurs if using `-m cProfile` instead of `-m profile`.

No such traceback occurs if the `from future import __annotations__` is removed from the file.

Possibly related to #39442.

----------
components: Library (Lib)
messages: 395762
nosy: wilcoxjay
priority: normal
severity: normal
status: open
title: from __future__ import annotations breaks profiler's handling of dataclasses
type: behavior
versions: Python 3.9

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44414>
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