psycopg2 stubs do not explicitly export anything and so can't be used for typechecking

[sh-at-cs]

Steps to reproduce

1. Create a new venv and install the relevant packages: pip3 install mypy psycopg2 types-psycopg2
2. Create a file example.py containing from psycopg2 import cursor
3. Typecheck this file with Mypy: mypy example.py

This will result in the following error:

example.py:1: error: Module "psycopg2" does not explicitly export attribute "cursor"  [attr-defined]

Suggested fix

Apparently, recent versions of Mypy need stub definitions to be explicitly exported via __all__, but this is missing from the psycopg2 stubs. So it's probably just to add those?

[srittau]

This matches the runtime behavior of psycopg:

Python 3.12.3 (main, Jul 31 2024, 17:43:48) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import psycopg2
>>> psycopg2.cursor
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'psycopg2' has no attribute 'cursor'

Other attributes that exist at runtime are correctly re-exported in the stubs.

At the moment, the best way to use cursor is to import it from psycopg2._psycopg. I admit that this is not ideal, and I'm open to the idea of defining clearly marked stubs-only aliases in __init__.pyi. (For example called _Cursor and _Connection.)

[sh-at-cs]

Oh I see, I completely misunderstood it then. Thanks!