flask_sqlalchemy：`__setattr__` 到 `DefaultMeta` 的错误

Question

重新构建 Docker 映像后，我开始收到以下错误：

$ docker run --rm -it python:3.8-slim /bin/bash
...
$ pip install flask_sqlalchemy
...
$ python -c "from flask_sqlalchemy import SQLAlchemy; SQLAlchemy()"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python3.8/site-packages/flask_sqlalchemy/__init__.py", line 715, in __init__
    self.Model = self.make_declarative_base(model_class, metadata)
  File "/usr/local/lib/python3.8/site-packages/flask_sqlalchemy/__init__.py", line 797, in make_declarative_base
    model.query_class = self.Query
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/ext/declarative/api.py", line 79, in __setattr__
    _add_attribute(cls, key, value)
  File "/usr/local/lib/python3.8/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

涉及的特定软件包的版本：

python -c "import sqlalchemy, flask_sqlalchemy; print(sqlalchemy.__version__, flask_sqlalchemy.__version__)"
1.3.18 # sqlalchemy
2.4.3 # flask_sqlalchemy

虽然我也遇到过版本1.3.17和2.4.1.

Answer 1

经过一些实验，问题似乎是由于python:3.8.3-slim和之间的一些变化造成的python:3.8.4-slim。

要重现，请注意这是有效的：

$ docker run --rm -it python:3.8.3-slim …

这不是：

docker run --rm -it python:3.8.4-slim …

看起来这个错误/修复是问题的原因：https : //bugs.python.org/issue39960