dbm: fix bytes handling (#9030)

Author: JelleZijlstra

stdlib/dbm/__init__.pyi

@@ -6,7 +6,7 @@ from typing_extensions import Literal, TypeAlias
 __all__ = ["open", "whichdb", "error"]
 
 _KeyType: TypeAlias = str | bytes
-_ValueType: TypeAlias = str | bytes
+_ValueType: TypeAlias = str | bytes | bytearray
 _TFlags: TypeAlias = Literal[
     "r",
     "w",

stdlib/dbm/dumb.pyi

@@ -10,6 +10,9 @@ _ValueType: TypeAlias = str | bytes
 
 error = OSError
 
+# This class doesn't exist at runtime. open() can return an instance of
+# any of the three implementations of dbm (dumb, gnu, ndbm), and this
+# class is intended to represent the common interface supported by all three.
 class _Database(MutableMapping[_KeyType, bytes]):
     def __init__(self, filebasename: str, mode: str, flag: str = ...) -> None: ...
     def sync(self) -> None: ...

stdlib/dbm/gnu.pyi

@@ -1,13 +1,13 @@
 import sys
-from _typeshed import Self
+from _typeshed import ReadOnlyBuffer, Self
 from types import TracebackType
 from typing import TypeVar, overload
 from typing_extensions import TypeAlias
 
 if sys.platform != "win32":
     _T = TypeVar("_T")
-    _KeyType: TypeAlias = str | bytes
-    _ValueType: TypeAlias = str | bytes
+    _KeyType: TypeAlias = str | ReadOnlyBuffer
+    _ValueType: TypeAlias = str | ReadOnlyBuffer
 
     open_flags: str
 
@@ -31,7 +31,7 @@ if sys.platform != "win32":
         @overload
         def get(self, k: _KeyType) -> bytes | None: ...
         @overload
-        def get(self, k: _KeyType, default: bytes | _T) -> bytes | _T: ...
+        def get(self, k: _KeyType, default: _T) -> bytes | _T: ...
         def keys(self) -> list[bytes]: ...
         def setdefault(self, k: _KeyType, default: _ValueType = ...) -> bytes: ...
         # Don't exist at runtime

stdlib/dbm/ndbm.pyi

@@ -1,13 +1,13 @@
 import sys
-from _typeshed import Self
+from _typeshed import ReadOnlyBuffer, Self
 from types import TracebackType
 from typing import TypeVar, overload
 from typing_extensions import TypeAlias
 
 if sys.platform != "win32":
     _T = TypeVar("_T")
-    _KeyType: TypeAlias = str | bytes
-    _ValueType: TypeAlias = str | bytes
+    _KeyType: TypeAlias = str | ReadOnlyBuffer
+    _ValueType: TypeAlias = str | ReadOnlyBuffer
 
     class error(OSError): ...
     library: str
@@ -27,7 +27,7 @@ if sys.platform != "win32":
         @overload
         def get(self, k: _KeyType) -> bytes | None: ...
         @overload
-        def get(self, k: _KeyType, default: bytes | _T) -> bytes | _T: ...
+        def get(self, k: _KeyType, default: _T) -> bytes | _T: ...
         def keys(self) -> list[bytes]: ...
         def setdefault(self, k: _KeyType, default: _ValueType = ...) -> bytes: ...
         # Don't exist at runtime