Python 3.9: use Optional instead of <type> | None

Not 100% sure why these didn't throw errors before, or why only some of
them do now, I'm sure it's something to do with
`from __future__ import annotations` interactions on when it stringizes
annotations.

structured/hint_types/arrays.py

@@ -20,7 +20,7 @@
     StaticStructArraySerializer,
     StructSerializer,
 )
-from ..type_checking import Annotated, Generic, S, Self, T, TypeVar, annotated
+from ..type_checking import Annotated, Generic, S, Self, T, TypeVar, annotated, Optional
 from ..utils import StructuredAlias
 from .basic_types import _SizeTypes
 
@@ -31,7 +31,7 @@ class Header:
     def __init__(
         self,
         count: int | StructSerializer[int],
-        data_size: StructSerializer[int] | None,
+        data_size: Optional[StructSerializer[int]],
     ) -> None:
         self.count = count
         self.data_size = data_size

structured/serializers/api.py

@@ -40,6 +40,7 @@
     ClassVar,
     Generic,
     Iterable,
+    Optional,
     ReadableBuffer,
     Self,
     Ss,
@@ -163,7 +164,7 @@ def is_final(self) -> bool:
         """
         return self.get_final() is not None
 
-    def get_final(self) -> Serializer | None:
+    def get_final(self) -> Optional[Serializer]:
         """Get the serializer (if any) that makes this serializer the final
         serializer.
         """
@@ -248,7 +249,7 @@ def __init__(self, serializers: tuple[Serializer, ...]) -> None:
             for serializer in serializers
         )
 
-    def get_final(self) -> Serializer | None:
+    def get_final(self) -> Optional[Serializer]:
         return self.serializers[-1].get_final()
 
     def prepack(self, partial_object: Any) -> Serializer:

structured/serializers/conditional.py

@@ -3,6 +3,7 @@
 to a Truthy value, the original serializer operates as normal. Otherwise,
 it acts as if the serializer was not there.
 """
+from __future__ import annotations
 
 __all__ = [
     'ConditionalSerializer',
@@ -14,6 +15,7 @@
     BinaryIO,
     Callable,
     Generic,
+    Optional,
     ReadableBuffer,
     Self,
     Ts,
@@ -52,7 +54,7 @@ def __init__(
                 f'{self.num_values}, got {expected}'
             )
 
-    def get_final(self) -> Serializer | None:
+    def get_final(self) -> Optional[Serializer]:
         return self.serializers[True].get_final()
 
     def with_byte_order(self, byte_order: ByteOrder) -> Self:

structured/serializers/strings.py

@@ -22,6 +22,7 @@
     BinaryIO,
     Callable,
     ClassVar,
+    Optional,
     ReadableBuffer,
     Self,
     Union,
@@ -368,7 +369,7 @@ def __init__(
         self.encoder = encoder
         self.decoder = decoder
 
-    def get_final(self) -> Serializer | None:
+    def get_final(self) -> Optional[Serializer]:
         return self.serializer.get_final()
 
     @property

structured/serializers/structured.py

@@ -12,6 +12,7 @@
     BinaryIO,
     ClassVar,
     Generic,
+    Optional,
     ReadableBuffer,
     TypeVar,
     WritableBuffer,
@@ -44,7 +45,7 @@ def __init__(self, obj_type: type[TStructured]) -> None:
         self.obj_type = obj_type
         self.size = 0
 
-    def get_final(self) -> Serializer | None:
+    def get_final(self) -> Optional[Serializer]:
         return self.obj_type.serializer.get_final()
 
     def pack(self, values: TStructured) -> bytes:

structured/serializers/tuples.py

@@ -14,6 +14,7 @@
     ClassVar,
     Generic,
     Iterable,
+    Optional,
     ReadableBuffer,
     Ts,
     Unpack,
@@ -28,7 +29,7 @@ class TupleSerializer(Generic[Unpack[Ts]], Serializer[Unpack[Ts]]):
     def __init__(self, serializers: Iterable[Serializer]) -> None:
         self.serializer = sum(serializers, NullSerializer())
 
-    def get_final(self) -> Serializer | None:
+    def get_final(self) -> Optional[Serializer]:
         return self.serializer.get_final()
 
     @property

structured/serializers/unions.py

@@ -19,6 +19,7 @@
     Callable,
     ClassVar,
     Iterable,
+    Optional,
     ReadableBuffer,
     WritableBuffer,
     annotated,
@@ -35,8 +36,8 @@ class AUnion(Serializer):
 
     num_values: ClassVar[int] = 1
     result_map: dict[Any, Serializer]
-    default: Serializer | None
-    _last_serializer: Serializer | None
+    default: Optional[Serializer]
+    _last_serializer: Optional[Serializer]
 
     def __init__(self, result_map: dict[Any, Any], default: Any = None) -> None:
         """result_map should be a mapping of possible return values from `decider`
@@ -52,7 +53,7 @@ def __init__(self, result_map: dict[Any, Any], default: Any = None) -> None:
         }
         self.size = 0
 
-    def get_final(self) -> Serializer | None:
+    def get_final(self) -> Optional[Serializer]:
         for serializer in self.result_map.values():
             if serializer.is_final():
                 return serializer.get_final()

structured/structured.py

@@ -53,7 +53,7 @@ def ispad(annotation: Any) -> bool:
     )
 
 
-def final_transform(base_type: Any, hint: Any) -> Serializer | None:
+def final_transform(base_type: Any, hint: Any) -> Optional[Serializer]:
     if isinstance(hint, Serializer):
         return hint
 
@@ -120,8 +120,8 @@ def get_structured_base(cls: type[Structured]) -> Optional[type[Structured]]:
 def gen_init(
     args: dict[str, Any],
     *,
-    globalsns: dict[str, Any] | None = None,
-    localsns: dict[str, Any] | None = None,
+    globalsns: Optional[dict[str, Any]] = None,
+    localsns: Optional[dict[str, Any]] = None,
 ) -> Callable:
     """Generates an __init__ method for a class.  `args` should be a mapping of
     arguments to type annotations to be used in the method definition.

structured/type_checking.py

@@ -115,7 +115,7 @@ def istuple(annotation: Any) -> TypeGuard[tuple]:
     return get_origin(annotation) in (tuple, Tuple)
 
 
-def get_tuple_args(annotation: Any, fixed_size: bool = True) -> tuple[Any, ...] | None:
+def get_tuple_args(annotation: Any, fixed_size: bool = True) -> Optional[tuple[Any, ...]]:
     """Get the arguments to a tuple type hint, or None if the annotation is not
     a tuple hint.  If `fixed_size` is True (default), then the tuple must be
     a fixed length tuple hint.