Error on windows 10 at briefcase dev

[lev007-ops]

Hello, I have such a project structure:

but when I write cd qr_generator in the telminal (vs code), and then briefcase dev, I get an error:

(.venv) C:\Users\Дом\Desktop\Py\PY\qr_generator\qr_generator>briefcase dev

[qr_generator] Starting in dev mode...
Traceback (most recent call last):
  File "C:\Users\Дом\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\Дом\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\qr_generator\src\qr_generator\__main__.py", line 4, in <module>
    main().main_loop()
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\qr_generator\src\qr_generator\app.py", line 41, in main
    return qrgenerator()
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga\app.py", line 272, in __init__
    self.factory = get_platform_factory(factory)
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga\platform.py", line 53, in get_platform_factory
    from toga_winforms import factory
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga_winforms\factory.py", line 1, in <module>
    from .app import App, MainWindow
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga_winforms\app.py", line 9, in <module>
    from .keys import toga_to_winforms_key
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga_winforms\keys.py", line 6, in <module>
    from .libs import WinForms
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga_winforms\libs\__init__.py", line 1, in <module>
    from .fonts import (  # noqa: F401
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga_winforms\libs\fonts.py", line 13, in <module>
    from .winforms import (
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\toga_winforms\libs\winforms.py", line 3, in <module>
    import clr
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\clr.py", line 6, in <module>
    load()
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\pythonnet\__init__.py", line 43, in load
    if func(''.encode("utf8")) != 0:
  File "C:\Users\Дом\Desktop\Py\PY\qr_generator\.venv\lib\site-packages\clr_loader\wrappers.py", line 20, in __call__
    return self._callable(ffi.cast("void*", buf_arr), len(buf_arr))
RuntimeError: cannot call null pointer pointer from cdata 'int(*)(void *, int)'

Unable to start application 'qr_generator'

The python version is 3.8.0. (it still costs 3.9, but venv is built on 3.8.0

Command line prefix - (.venv)

Python -V command: Python 3.8.0

What to do on windows 10?

[freakboy3742]

This isn't an error that I've seen before.

Can I ask what version of Toga you're using? You can find this out from pip freeze. Also - can you confirm if you received any error messages when installing pythonnet?

I'm also a little unclear what you're saying about "3.9" - are you saying that you see the same error on a Python 3.9 venv as you do with 3.8?

[lev007-ops]

Hello, I solved the problem by installing a stable version of pythonnet.

The system has 2 mounted pitons: 3.9, 3.8. But I created venv using: path to python3.8 -m venv .venv