The initial problem, I am developing on the flask app framework and I was trying out blueprint template and it update my version of python I think to 3.8.4 and this new error appear. I was on python 3.8.3
flask run
outputted a complicated error a python type Error.
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.8_3.8.1264.0_x64__qbz5n2kfra8p0\lib\runpy.py", line 194, in _run_module_as_main
return _run_code(code, main_globals, None,
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.8_3.8.1264.0_x64__qbz5n2kfra8p0\lib\runpy.py", line 87, in _run_code
exec(code, run_globals)
File "D:\Openvessel\vessel-app\vessel_env\Scripts\flask.exe\__main__.py", line 9, in <module>
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask\cli.py", line 966, in main
cli.main(prog_name="python -m flask" if as_module else None)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask\cli.py", line 586, in main
return super(FlaskGroup, self).main(*args, **kwargs)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\click\core.py", line 782, in main
rv = self.invoke(ctx)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\click\core.py", line 1259, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\click\core.py", line 1066, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\click\core.py", line 610, in invoke
return callback(*args, **kwargs)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\click\decorators.py", line 73, in new_func
return ctx.invoke(f, obj, *args, **kwargs)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\click\core.py", line 610, in invoke
return callback(*args, **kwargs)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask\cli.py", line 848, in run_command
app = DispatchingApp(info.load_app, use_eager_loading=eager_loading)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask\cli.py", line 305, in __init__
self._load_unlocked()
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask\cli.py", line 330, in _load_unlocked
self._app = rv = self.loader()
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask\cli.py", line 388, in load_app
app = locate_app(self, import_name, name)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask\cli.py", line 240, in locate_app
__import__(module_name)
File "D:\Openvessel\vessel-app\Back-end\app.py", line 1, in <module>
from vessel_app import create_app
File "D:\Openvessel\vessel-app\Back-end\vessel_app\__init__.py", line 21, in <module>
db = SQLAlchemy()
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask_sqlalchemy\__init__.py", line 716, in __init__
self.Model = self.make_declarative_base(model_class, metadata)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\flask_sqlalchemy\__init__.py", line 798, in make_declarative_base
model.query_class = self.Query
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\sqlalchemy\ext\declarative\api.py", line 79, in __setattr__
_add_attribute(cls, key, value)
File "d:\openvessel\vessel-app\vessel_env\lib\site-packages\sqlalchemy\ext\declarative\base.py", line 802, in _add_attribute
type.__setattr__(cls, key, value)
TypeError: can't apply this __setattr__ to DefaultMeta object
My last guess is that its or its the python version 3.8.4 slim has this error.
File "D:\Openvessel\vessel-app\Back-end\vessel_app\__init__.py", line 21, in <module>
db = SQLAlchemy()
This looks like an issue that was introduced into the python language.
To fix this:
You can revert the version of python you are building with, or if you are using docker, fix the python image temporarily using python:3.8.3-slim or an equivalent image. You can also wait until the fix is out.
You can see the related pull request here: https://github.com/python/cpython/pull/21473
Introduced here: https://bugs.python.org/issue39960
Patch bug here: https://bugs.python.org/issue41295
Another issue in an unrelated package that is the same error: flask_sqlalchemy: error with `__setattr__` to `DefaultMeta`
Edit: A newer version with the fix introduced is out. Check out any image of python:3.8.5 +.