fix import

Signed-off-by: nstarman <nstarkman@protonmail.com>

astropy/units/quantity.py

@@ -21,7 +21,7 @@
                    UnitBase, UnitsError, UnitConversionError, UnitTypeError)
 from .utils import is_effectively_unity
 from .format.latex import Latex
-from .typing import Annotated
+from ._typing import Annotated
 from astropy.utils.compat.misc import override__dir__
 from astropy.utils.exceptions import AstropyDeprecationWarning, AstropyWarning
 from astropy.utils.misc import isiterable
@@ -337,11 +337,31 @@ def __class_getitem__(cls, unit_annotation):
                 >>> Quantity[Unit("s")]
                 Annotated[<class 'astropy.units.quantity.Quantity'>, Unit("s")]
 
+            This is equivalent, but easier than, manually creating the
+            annotation. In Python 3.9+ ``Annotated`` is built into
+            :mod:`~typing`. For older python versions, the optional dependency
+            :mod:`~typing_extensions` provides the same class. When neither are
+            available we default to a run-time only compatibility class (in
+            ``astropy.units._typing``) with reduced functionality. The best
+            implementation is automatically detected and used.
+
+                >>> from astropy.units._typing import Annotated  # imports best
+                >>> Annotated[Quantity, Unit("s")]
+                Annotated[<class 'astropy.units.quantity.Quantity'>, Unit("s")]
+
+            With Python 3.9+ or :mod:`~typing_extensions` Quantity types
+            can be used as static type annotations.
+
+                >>> def func(x: Quantity[u.kpc]) -> Quantity[u.m]:
+                ...     return x << u.m
+
             """
             if isinstance(unit_annotation, tuple):  # unit and annotations
                 unit = unit_annotation[0]
                 if len(unit_annotation) > 1:  # multiple metadata  # TODO
-                    raise NotImplementedError("Multiple metadata not yet supported.")
+                    raise NotImplementedError(
+                        "Multiple metadata not yet supported."
+                    )
                 else:  # just unit
                     annotations = ()
             else:  # just unit