fix(typing): Avoid false positives on nw.__getattr__ (#3333)

Author: dangotbanned

narwhals/__init__.py

@@ -177,13 +177,17 @@
 ]
 
 
-def __getattr__(name: _t.Literal["__version__"]) -> str:  # type: ignore[misc]
-    if name == "__version__":
-        global __version__  # noqa: PLW0603
+if not _t.TYPE_CHECKING:
 
-        from importlib import metadata
+    def __getattr__(name: str) -> _t.Any:
+        if name == "__version__":
+            global __version__  # noqa: PLW0603
 
-        __version__ = metadata.version(__name__)
-        return __version__
-    msg = f"module {__name__!r} has no attribute {name!r}"
-    raise AttributeError(msg)
+            from importlib import metadata
+
+            __version__ = metadata.version(__name__)
+            return __version__
+        msg = f"module {__name__!r} has no attribute {name!r}"
+        raise AttributeError(msg)
+else:  # pragma: no cover
+    ...

tests/version_test.py

@@ -1,9 +1,13 @@
 from __future__ import annotations
 
 import re
+from collections.abc import Callable
 from importlib.metadata import distribution
 from os import environ
 from pathlib import Path
+from typing import TYPE_CHECKING, Any
+
+import pytest
 
 import narwhals as nw
 from narwhals._utils import parse_version
@@ -35,3 +39,20 @@ def test_package_version() -> None:
         assert version_comp <= parse_version(pyproject_version)
     dist_version = distribution("narwhals").version
     assert version == dist_version
+
+
+def test_package_getattr() -> None:
+    pytest.importorskip("typing_extensions")
+    from typing_extensions import assert_type
+
+    ok = nw.__version__
+    assert_type(ok, str)
+    also_ok = nw.all
+    assert_type(also_ok, Callable[[], nw.Expr])
+
+    if TYPE_CHECKING:
+        bad = nw.not_real  # type: ignore[attr-defined]
+        assert_type(bad, Any)
+
+    with pytest.raises(AttributeError):
+        very_bad = nw.not_real  # type: ignore[attr-defined]  # noqa: F841