Dataclass takes no arguments in a subinterpreter in 3.12

[peterebden]

Bug report

Bug description:

In 3.12, when I construct an instance of a dataclass in a subinterpreter, I get an "X takes no arguments" error, for cases that work fine in the main interpreter.

A fairly minimal code example:

#include <stdio.h>

#include <Python.h>

const char* code = "\n\
from dataclasses import dataclass\n\
\n\
@dataclass\n\
class MyClass:\n\
 id: str\n\
\n\
c = MyClass(id='abc')\n\
print(c)\n\
";

int main(int argc, char** argv){
 Py_InitializeEx(0);
 printf("Python version: ");
 fflush(stdout);
 PyRun_SimpleString("import sys; print(sys.version)");
 PyThreadState* main_thread = PyThreadState_Get();

 printf("In main interpreter:\n");
 PyRun_SimpleString(code);

 PyThreadState* interpreter_thread = Py_NewInterpreter();
 printf("\nIn subinterpreter:\n");
 PyRun_SimpleString(code);
 Py_EndInterpreter(interpreter_thread);

 PyThreadState_Swap(main_thread);
 Py_Finalize();
 return 0;
}

Compiled with gcc -o py_dataclass py_dataclass.c -I /usr/include/python3.11 -lpython3.11 I get the expected:

Python version: 3.11.5 (main, Aug 25 2023, 13:19:50) [GCC 11.4.0]
In main interpreter:
MyClass(id='abc')

In subinterpreter:
MyClass(id='abc')

Compiled with gcc -o py_dataclass py_dataclass.c -I /usr/include/python3.12 -lpython3.12 I get:

Python version: 3.12.0 (main, Oct 2 2023, 15:04:50) [GCC 11.4.0]
In main interpreter:
MyClass(id='abc')

In subinterpreter:
Traceback (most recent call last):
 File "<string>", line 8, in <module>
TypeError: MyClass() takes no arguments

This is using the python3.11-dev and python3.12-dev packages from the deadsnakes PPA.

I'm a little lost about what the interaction between the subinterpreter and the dataclass is that would cause this. The non-mangled Python code is just

from dataclasses import dataclass

@dataclass
class MyClass:
 id: str

c = MyClass(id='abc')
print(c)

Let me know if there's any more info I can provide!

CPython versions tested on:

3.11, 3.12

Operating systems tested on:

Linux

[peterebden]

An interesting datapoint; the following code does work as expected in the subinterpreter:

from dataclasses import dataclass

@dataclass
class MyClass:
 id: str

@dataclass 
class MySubClass(MyClass):
 pass

c = MySubClass(id='abc')
print(c)

[AA-Turner]

cc: @ericsnowcurrently

[ericsnowcurrently]

Any ideas, @ericvsmith?

[ericsnowcurrently]

FWIW, it seems to work fine on main. I was able to reproduce the failure on 3.12:

from test.support import interpreters

interp = interpreters.create()
interp.run("""if True:
 from dataclasses import dataclass

 @dataclass
 class MyClass:
 id: str

 c = MyClass(id='abc')
 print(c)
 """)

[peterebden]

Ah nice, I didn't know that test module was available to try it out in pure Python.

Also working for me at head, same for our internal usage (which is a bit more complex than the reduced example here - there's something else going wrong there which I'm still digging through).

[ericvsmith]

I have no idea what's going on there. I don't have handy access to my dev box right now, but maybe inspecting the signature for MyClass.__init__ will shed some light.

[graingert]

bisected to ba65a06 on 3.12
looks like it was fixed again on main in b72947a