Debugging class with modified __getattribute__ freezes debugpy

[fireattack]

Before creating a new issue, please check the FAQ to see if your question is answered there.

Environment data

• debugpy version: the one bundled with VS Code extension ms-python.debugpy-2025.0.0-win32-x64
• OS and version: Windows 10
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.11
• Using VS Code or Visual Studio: VS Code

Actual behavior

debugpy throws an error

Expected behavior

It should not raise an error in debugpy or cause VS Code debugging to freeze.

Steps to reproduce:

1. Create a file with the following content:

class KillDebugpy():
    def __getattribute__(self, _):
        return self

a = KillDebugpy()
print('Done')

2. Add a breakpoint in front of print()
3. Start debugging the file in VS Code.
4. Observe the following error in terminal, and it freezes VS Code debugging interface (you cannot stop it in UI.)

> cmd /C "c:\Users\{masked}\AppData\Local\Programs\Python\Python311\python.exe c:\Users\{masked}\.vscode\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\launcher 11138 -- D:\sync\code\python\trysail\_test4.py "
0.77s - Error processing internal command.
Traceback (most recent call last):
  File "c:\Users\{masked}\.vscode\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\pydevd.py", line 2245, in _do_wait_suspend
    internal_cmd.do_it(self)
  File "c:\Users\{masked}\.vscode\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py", line 565, in do_it
    self.method(dbg, *self.args, **self.kwargs)
  File "c:\Users\{masked}\.vscode\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_constants.py", line 531, in new_func
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "c:\Users\{masked}\.vscode\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py", line 813, in internal_get_variable_json
    py_db.writer.add_command(NetCommand(CMD_RETURN, 0, variables_response, is_json=True))
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\Users\{masked}\.vscode\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_net_command.py", line 80, in __init__
    text = json.dumps(as_dict)
           ^^^^^^^^^^^^^^^^^^^
  File "c:\Users\{masked}\AppData\Local\Programs\Python\Python311\Lib\json\__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\Users\{masked}\AppData\Local\Programs\Python\Python311\Lib\json\encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\Users\{masked}\AppData\Local\Programs\Python\Python311\Lib\json\encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
  File "c:\Users\{masked}\AppData\Local\Programs\Python\Python311\Lib\json\encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type <__main__.KillDebugpy object at 0x00000179EC1F9E50> is not JSON serializable

This bug was first observed in real-world code (see: mikf/gallery-dl#6582 (comment)), and I then created a minimal reproducible example based on it.

[rchiodo]

Thanks, we could probably handle infinite __getattribute__ better.

I think this would do it (in pydevd_pydevd_bundle\pydevd_net_command.py)

            try:
                text = json.dumps(as_dict)
            except TypeError:
                text = json.dumps(as_dict, default=lambda o: str(o))

[rchiodo]

This issue should be fixed in the latest build of debugpy. It should ship with VS code in a future version of the Python Debugger Extension or you can install your own debugpy from pypi