Introduce ReadableBuffer and WriteableBuffer Union aliases

Since typing doesn't yet have a way to express buffer protocol objects
(python/typing#593), various interfaces have ended up with a mish-mash
of options: some list just bytes (or just bytearray, when writable),
some include mmap, some include memoryview, I think none of them include
array.array even though it's explicitly mentioned as bytes-like, etc. I
ran into problems because RawIOBase.readinto didn't allow for
memoryview.

To allow for some uniformity until the fundamental issue is resolved,
I've introduced _typeshed.ReadableBuffer and _typeshed.WriteableBuffer,
and applied them in stdlib/3/io.pyi as an example. If these get rolled
out in more places, it will mean that we have only one place where they
have to get tweaked in future, or swapped out for a public protocol.

This unfortunately does have the potential to break code that inherits
from RawIOBase/BufferedIOBase and overrides these methods, because the
base method is now more general and so the override now needs to accept
these types as well (which is why I've also updated gzip and lzma).
However, it should be a reasonably easy fix, and will make the
downstream annotations more correct.

I'm not 100% happy with the names: bytes-like is slightly stricter than
just buffer protocol (it must be able to export a C-contiguous buffer),
but in practice I'd be surprised if there are types for which there is a
difference at static analysis time (e.g. not every memoryview instance
is bytes-like, but that's a property of instances, not types).

stdlib/2and3/_typeshed/__init__.pyi

@@ -12,6 +12,8 @@
 # If on Python versions < 3.10 and "from __future__ import annotations"
 # is not used, types from this module must be quoted.
 
+import array
+import mmap
 import sys
 from typing import Protocol, Text, TypeVar, Union
 from typing_extensions import Literal
@@ -67,3 +69,6 @@ class SupportsReadline(Protocol[_T_co]):
     def readline(self, __length: int = ...) -> _T_co: ...
 class SupportsWrite(Protocol[_T_contra]):
     def write(self, __s: _T_contra) -> int: ...
+
+ReadableBuffer = Union[bytes, bytearray, memoryview, array.array, mmap.mmap]
+WriteableBuffer = Union[bytearray, memoryview, array.array, mmap.mmap]

stdlib/3/gzip.pyi

@@ -2,7 +2,7 @@ import sys
 import zlib
 from typing import IO, Optional, TextIO, Union, overload
 import _compression
-from _typeshed import AnyPath
+from _typeshed import AnyPath, ReadableBuffer
 from typing_extensions import Literal
 
 _OpenBinaryMode = Literal["r", "rb", "a", "ab", "w", "wb", "x", "xb"]
@@ -63,7 +63,7 @@ class GzipFile(_compression.BaseStream):
     @property
     def mtime(self) -> Optional[int]: ...
     crc: int
-    def write(self, data: bytes) -> int: ...
+    def write(self, data: ReadableBuffer) -> int: ...
     def read(self, size: Optional[int] = ...) -> bytes: ...
     def read1(self, size: int = ...) -> bytes: ...
     def peek(self, n: int) -> bytes: ...

stdlib/3/io.pyi

@@ -6,8 +6,7 @@ import codecs
 import sys
 from mmap import mmap
 from types import TracebackType
-
-_bytearray_like = Union[bytearray, mmap]
+from _typeshed import ReadableBuffer, WriteableBuffer
 
 DEFAULT_BUFFER_SIZE: int
 
@@ -42,7 +41,7 @@ class IOBase:
     def tell(self) -> int: ...
     def truncate(self, __size: Optional[int] = ...) -> int: ...
     def writable(self) -> bool: ...
-    def writelines(self, __lines: Iterable[Union[bytes, bytearray]]) -> None: ...
+    def writelines(self, __lines: Iterable[ReadableBuffer]) -> None: ...
     def readline(self, __size: Optional[int] = ...) -> bytes: ...
     def __del__(self) -> None: ...
     @property
@@ -51,16 +50,16 @@ class IOBase:
 
 class RawIOBase(IOBase):
     def readall(self) -> bytes: ...
-    def readinto(self, __buffer: bytearray) -> Optional[int]: ...
-    def write(self, __b: Union[bytes, bytearray]) -> Optional[int]: ...
+    def readinto(self, __buffer: WriteableBuffer) -> Optional[int]: ...
+    def write(self, __b: ReadableBuffer) -> Optional[int]: ...
     def read(self, __size: int = ...) -> Optional[bytes]: ...
 
 class BufferedIOBase(IOBase):
     raw: RawIOBase  # This is not part of the BufferedIOBase API and may not exist on some implementations.
     def detach(self) -> RawIOBase: ...
-    def readinto(self, __buffer: _bytearray_like) -> int: ...
-    def write(self, __buffer: Union[bytes, bytearray]) -> int: ...
-    def readinto1(self, __buffer: _bytearray_like) -> int: ...
+    def readinto(self, __buffer: WriteableBuffer) -> int: ...
+    def write(self, __buffer: ReadableBuffer) -> int: ...
+    def readinto1(self, __buffer: WriteableBuffer) -> int: ...
     def read(self, __size: Optional[int] = ...) -> bytes: ...
     def read1(self, __size: int = ...) -> bytes: ...
 
@@ -75,7 +74,7 @@ class FileIO(RawIOBase, BinaryIO):
         closefd: bool = ...,
         opener: Optional[Callable[[Union[int, str], str], int]] = ...
     ) -> None: ...
-    def write(self, __b: bytes) -> int: ...
+    def write(self, __b: ReadableBuffer) -> int: ...
     def read(self, __size: int = ...) -> bytes: ...
     def __enter__(self: _T) -> _T: ...
 
@@ -105,7 +104,7 @@ class BufferedReader(BufferedIOBase, BinaryIO):
 class BufferedWriter(BufferedIOBase, BinaryIO):
     def __enter__(self: _T) -> _T: ...
     def __init__(self, raw: RawIOBase, buffer_size: int = ...) -> None: ...
-    def write(self, __buffer: Union[bytes, bytearray]) -> int: ...
+    def write(self, __buffer: ReadableBuffer) -> int: ...
 
 class BufferedRandom(BufferedReader, BufferedWriter):
     def __enter__(self: _T) -> _T: ...

stdlib/3/lzma.pyi

@@ -1,6 +1,6 @@
 import io
 from typing import IO, Any, Mapping, Optional, Sequence, TextIO, TypeVar, Union, overload
-from _typeshed import AnyPath
+from _typeshed import AnyPath, ReadableBuffer
 from typing_extensions import Literal
 
 _OpenBinaryWritingMode = Literal["w", "wb", "x", "xb", "a", "ab"]
@@ -88,7 +88,7 @@ class LZMAFile(io.BufferedIOBase, IO[bytes]):
     def read(self, size: Optional[int] = ...) -> bytes: ...
     def read1(self, size: int = ...) -> bytes: ...
     def readline(self, size: Optional[int] = ...) -> bytes: ...
-    def write(self, data: bytes) -> int: ...
+    def write(self, data: ReadableBuffer) -> int: ...
     def seek(self, offset: int, whence: int = ...) -> int: ...
     def tell(self) -> int: ...