MYPYPATH should override mypy_path in config file (not extend it)

Feature

The MYPYPATH environment variable should override the mypy_path config file option (not extend it).

Pitch

I propose the ability to override the mypy_path config file option with the the MYPYPATH environment variable. To make Visual Studio Code work with the Mypy extension for namespace packages, it is necessary to set mypy_path and explicit_package_bases, whereas I would like to disable the mypy_path option when running Tox (to typecheck the installed package). It is usually the case that environment variables have higher precedence over config file options, and this change would make Mypy consistent with the expected behavior.

Commencez par localiser l’analyse de la configuration de mypy et la gestion existante de MYPYPATH et de mypy_path, puis recherchez les tests couvrant la priorité de la configuration ou les variables d’environnement. Confirmez le comportement actuel avant de le modifier. La tâche est terminée lorsque MYPYPATH remplace la valeur de mypy_path du fichier de configuration, tandis que le comportement existant et les options associées restent couverts par des tests.