How should Pyright consider typing stubs with try-excepted imports?

[decorator-factory]

immutables repo: https://github.com/MagicStack/immutables/blob/master/immutables/__init__.py

has this code in __init__.py:

try:
    from ._map import Map
except ImportError:
    from .map import Map

The project has a _map.pyi, but no map.pyi. Pyright thinks that only map is ever imported, so it doesn't use _map.pyi.

This is fixed by:

try:
    from ._map import Map
except ImportError:
    if TYPE_CHECKING:
        from ._map import Map
    else:
        from .map import Map

or:

if TYPE_CHECKING:
    from ._map import Map
else:
    try:
        from ._map import Map
    except ImportError:
        from .map import Map

but maybe Pyright should somehow use _map's typing stub in that case? Or would you say that libraries should just use the second variant, or provide typing stubs for module instead of _module?

[erictraut]

Conditional (dynamic) imports are very difficult for a static analyzer. When resolving an import symbol, Pyright uses the last declaration of the symbol in the file regardless of whether the import statement is in an if/else or try/except block. If that order doesn't work for you, you can use a a TYPE_CHECKING conditional to hide declarations that you don't want pyright to consider.

Another option is to create a local stub alias. In your case you could create a map.pyi that re-exports all the symbols from _map.pyi.

[decorator-factory]

That makes sense. Thank you!