create_engine 中的 Flask SQLAlchemy KeyError 'False'

Question

I have a flask app that connects with mysql using sqlalchemy. A strange error happens on DB query.

`Traceback (most recent call last): File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/util/_collections.py", line 1008, in call return self.registry[key] KeyError: <greenlet.greenlet object at 0x7f22a0936a90 (otid=0x7f22a08ef100) current active started main>

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File "/home/Desktop/work/nesting-app/server/users/routes.py", line 28, in register_new_user if form.validate_on_submit(): File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/flask_wtf/form.py", line 100, in validate_on_submit return self.is_submitted() and self.validate() File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/wtforms/form.py", line 318, in validate return super(Form, self).validate(extra) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/wtforms/form.py", line 150, in validate if not field.validate(self, extra): File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/wtforms/fields/core.py", line 226, in validate stop_validation = self._run_validation_chain(form, chain) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/wtforms/fields/core.py", line 246, in _run_validation_chain validator(form, self) File "/home/Desktop/work/nesting-app/server/users/forms .py", line 43, in validate_email user = User.query.filter_by(email=email.data).first() File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/flask_sqlalchemy/ init .py", line 552, in get return type.query_class(mapper, session=self.sa.session()) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/orm/scoping.py", line 47, in call sess = self.registry() File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/util/ collections.py", line 1010, in call return self.registry.setdefault(key, self.createfunc()) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 4171, in call return self.class (**local_kw) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/flask_sqlalchemy/ init .py", line 176, in init bind = options.pop('bind', None) or db.engine File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/flask_sqlalchemy/ init .py", line 998, in engi ne return self.get_engine() File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/flask_sqlalchemy/ init .py", line 1017, in get_engine return connector.get_engine() File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/flask_sqlalchemy/ init .py", line 594, in get_engine self._engine = rv = self._sa.create_engine(sa_url, options) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/flask_sqlalchemy/ init .py", line 1027, in create_engine return sqlalchemy.create_engine(sa_url, **engine_opts) File "", line 2, in create_engine File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/util/deprecations.py", line 298, in warned return fn(*args, **kwargs) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/engine/create.py", line 661, in create_engine engine = engineclass(pool, dialect, u, **engine_args) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/engine/base. py", line 2758, in init self.echo = echo File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/log.py", line 225, in set instance_logger(instance, echoflag=value) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/log.py", line 202, in instance_logger logger = InstanceLogger(echoflag, name) File "/home/Desktop/work/nesting-app/env/lib/python3.8/site-packages/sqlalchemy/log.py", line 103, in init if self._echo_map[echo] <= logging.INFO and not self.logger.handlers: KeyError: 'False' `

Here is the config.py

from os import environ, path
from dotenv import load_dotenv
from pathlib import Path

BASE_DIR = Path(__file__).resolve().parent.parent
load_dotenv(path.join(BASE_DIR, '.env'))


class Config:
    SECRET_KEY = environ.get('SECRET_KEY')
    SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://user:password@127.0.0.1:3306/dbname'
    # SQLALCHEMY_ECHO: When set to 'True', Flask-SQLAlchemy will log all database
    # activity to Python's stderr for debugging purposes.
    SQLALCHEMY_ECHO = environ.get('SQLALCHEMY_ECHO')
    #  To suppress the warning "this option takes a lot of system resources" set
    SQLALCHEMY_TRACK_MODIFICATIONS = environ.get('SQLALCHEMY_TRACK_MODIFICATIONS')

Here is the init.py

db = SQLAlchemy()
bcrypt = Bcrypt()
login_manager = LoginManager()
login_manager.login_view = 'users.login'
mail = Mail()
csrf = CSRFProtect()


def create_app(config_class=Config):
    flask_app = Flask(__name__)
    flask_app.config.from_object(config_class)

    db.init_app(flask_app)
    bcrypt.init_app(flask_app)
    login_manager.init_app(flask_app)
    mail.init_app(flask_app)
    csrf.init_app(flask_app)

I have tried with different connection strings:

SQLALCHEMY_DATABASE_URI=mysql+mysqlconnector://user:pass@localhost:3306/dbname

SQLALCHEMY_DATABASE_URI=mysql+mysqlconnector://user:pass@localhost/dbname

SQLALCHEMY_DATABASE_URI=mysql+mysqlconnector://user:pass@127.0.0.1:3306/dbname

Thank you for any help.

Answer 1

The echo flag for SQLAlchemy's create_engine function accepts a limited set of values: None , False , True , "debug" ( source ).

The traceback shows that the string "False" is being passed: KeyError: 'False' . In fact, the error can be reproduced by passing any string (except "debug") as the value of create_engine 's echo flag:

create_engine('sqlite://', echo='banana')

results in

Traceback (most recent call last):
   ...
KeyError: 'banana'

At a guess, the problem is that

SQLALCHEMY_ECHO = environ.get('SQLALCHEMY_ECHO')

does not consider that environment variables are always strings. Something like this might be better:

SQLALCHEMY_ECHO = environ.get('SQLALCHEMY_ECHO') in ('1', 'True')

as it will result in a boolean value being assigned.