Use TypeGuards and fix type issues

src/marshmallow/fields.py

@@ -35,7 +35,6 @@
     ValidationError,
     _FieldInstanceResolutionError,
 )
-from marshmallow.utils import is_aware, is_collection
 from marshmallow.validate import And, Length
 
 if typing.TYPE_CHECKING:
@@ -501,9 +500,9 @@ def __init__(
         **kwargs: Unpack[_BaseFieldKwargs],
     ):
         # Raise error if only or exclude is passed as string, not list of strings
-        if only is not None and not is_collection(only):
+        if only is not None and not utils.is_sequence_but_not_string(only):
             raise StringNotCollectionError('"only" should be a collection of strings.')
-        if not is_collection(exclude):
+        if not utils.is_sequence_but_not_string(exclude):
             raise StringNotCollectionError(
                 '"exclude" should be a collection of strings.'
             )
@@ -818,7 +817,7 @@ def _deserialize(
         data: typing.Mapping[str, typing.Any] | None,
         **kwargs,
     ) -> tuple:
-        if not utils.is_collection(value):
+        if not utils.is_sequence_but_not_string(value):
             raise self.make_error("invalid")
 
         self.validate_length(value)
@@ -1322,7 +1321,7 @@ def __init__(
 
     def _deserialize(self, value, attr, data, **kwargs) -> dt.datetime:
         ret = super()._deserialize(value, attr, data, **kwargs)
-        if is_aware(ret):
+        if utils.is_aware(ret):
             if self.timezone is None:
                 raise self.make_error(
                     "invalid_awareness",
@@ -1359,7 +1358,7 @@ def __init__(
 
     def _deserialize(self, value, attr, data, **kwargs) -> dt.datetime:
         ret = super()._deserialize(value, attr, data, **kwargs)
-        if not is_aware(ret):
+        if not utils.is_aware(ret):
             if self.default_timezone is None:
                 raise self.make_error(
                     "invalid_awareness",

src/marshmallow/utils.py

@@ -16,15 +16,13 @@
 
 from marshmallow.constants import missing
 
-# TODO: Use TypeGuard for predicate functions
 
-
-def is_generator(obj) -> bool:
+def is_generator(obj) -> TypeGuard[typing.Generator]:
     """Return True if ``obj`` is a generator"""
     return inspect.isgeneratorfunction(obj) or inspect.isgenerator(obj)
 
 
-def is_iterable_but_not_string(obj) -> bool:
+def is_iterable_but_not_string(obj) -> TypeGuard[typing.Iterable]:
     """Return True if ``obj`` is an iterable object that isn't a string."""
     return (hasattr(obj, "__iter__") and not hasattr(obj, "strip")) or is_generator(obj)
 
@@ -34,7 +32,7 @@ def is_sequence_but_not_string(obj) -> TypeGuard[Sequence]:
     return isinstance(obj, Sequence) and not isinstance(obj, (str, bytes))
 
 
-def is_collection(obj) -> bool:
+def is_collection(obj) -> TypeGuard[typing.Iterable]:
     """Return True if ``obj`` is a collection type, e.g list, tuple, queryset."""
     return is_iterable_but_not_string(obj) and not isinstance(obj, Mapping)