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After re-building a Docker image, I've started to get the following error:
$ 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
The versions of the specific packages involved:
python -c "import sqlalchemy, flask_sqlalchemy; print(sqlalchemy.__version__, flask_sqlalchemy.__version__)"
1.3.18 # sqlalchemy
2.4.3 # flask_sqlalchemy
Although I've also experienced the error with versions 1.3.17 and 2.4.1.
905
Step 1 - Install the Flask-SQLAlchemy extension. Step 2 - You need to import the SQLAlchemy class from this module. Step 3 - Now create a Flask application object and set the URI for the database to use.
This error message indicates that the index.html template does not exist. To fix this, you’ll create a base.html template file other templates will inherit from to avoid code repetition, then an index.html template that extends the base template. Create the templates directory, which is the directory where Flask looks for template files.
Using raw SQL in the Flask Web application to perform CRUD operations on the database can be cumbersome. Instead, SQLAlchemy, the Python Toolkit is a powerful OR Mapper, which provides application developers with the full functionality and flexibility of SQL.
Flask is a lightweight Python web framework that provides useful tools and features for creating web applications in the Python Language. It gives developers flexibility and is an accessible framework for new developers because you can build a web application quickly using only a single Python file.
After some experimentation, it seems like the issue is due to some change between python:3.8.3-slim and python:3.8.4-slim.
To reproduce, notice that this works:
$ docker run --rm -it python:3.8.3-slim …
Where this does not:
docker run --rm -it python:3.8.4-slim …
It looks like this bug/fix is the cause of the issue: https://bugs.python.org/issue39960
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