SQLAlchemy: Instance of 'sessionmaker' has no 'begin' member

[neilmunday]

Bug description

When using SQL Alchemy's sessionmaker.begin functionailty (ref: https://docs.sqlalchemy.org/en/14/orm/session_api.html#sqlalchemy.orm.sessionmaker.begin), pylint outputs the following errors:

E1101: Instance of 'sessionmaker' has no 'begin' member (no-member)

Example:

from sqlalchemy.orm import sessionmaker

Session = sessionmaker(some_engine)

with Session.begin() as session:
    session.add(some_object)

Configuration

No response

Command used

pylint bin/populate-db.py

Pylint output

************* Module populate-db
bin/populate-db.py:120:9: E1101: Instance of 'sessionmaker' has no 'begin' member (no-member)
bin/populate-db.py:156:9: E1101: Instance of 'sessionmaker' has no 'begin' member (no-member)
bin/populate-db.py:210:9: E1101: Instance of 'sessionmaker' has no 'begin' member (no-member)

Expected behavior

pylint should not output errors for sqlalchemy.orm.sessionmaker.begin.

Pylint version

pylint 2.14.3
astroid 2.11.6
Python 3.9.12 (main, Mar 25 2022, 00:00:00)
[GCC 11.2.1 20220127 (Red Hat 11.2.1-9)]

OS / Environment

Fedora 34, BASH shell.

Additional dependencies

No response

[jacobtylerwalls]

We have several open issues for SQLAlchemy, which points to the need for a third party project for this inspired by pylint-django etc.

Here, we just don't know that sessionmaker() is a class factory and returns instances of other classes. Poor pylint just knows it to be:
<Instance of sqlalchemy.orm.session.sessionmaker at 0x4576244016>, which definitely doesn't have begin.

As a workaround, you can invoke pylint with --ignored-classes='sqlalchemy.orm.session.sessionmaker'.

[neilmunday]

@jacobtylerwalls thank you for the explanation and for the info on how to workaround the issue.

[CarliJoy]

Same is true for

from sqlalchemy import func

print(func.count(1))

Leads to

testing.py:3:6: E1102: func.count is not callable (not-callable)

So here again astroid/pylint isn't able to determine the correct stuff.

[scribblemaniac]

Poor pylint just knows it to be:
<Instance of sqlalchemy.orm.session.sessionmaker at 0x4576244016>, which definitely doesn't have begin.

@jacobtylerwalls Either I'm missing something, or that's exactly what this is: https://github.com/sqlalchemy/sqlalchemy/blob/ca813b33f5447e592eace3117f3521a007f30b60/lib/sqlalchemy/orm/session.py#L5057

[jenstroeger]

@CarliJoy for “normal” SQL functions — have you tried

>>> import sqlalchemy.sql.functions
>>> sqlalchemy.sql.functions.count
<class 'sqlalchemy.sql.functions.count'>

instead of the func function generator?

@neilmunday @jacobtylerwalls oddly enough, this one lints just fine:

with Session() as session:
    with session.begin():
        ...

For more details on the difference between Session.begin() and Session().begin() see the sessionmaker() docs.

[jacobtylerwalls]

Thanks for the workaround!

Based on the helpful link from @scribblemaniac, I think @overload is to blame. So this is a duplicate of pylint-dev/astroid#1015 / #5712.