Widened type annotations to accept IO[bytes] in file streams

agronholm · agronholm · commit 602f6606dcf3 · 2026-03-22T22:43:54.000+02:00
Fixes #1078. Closes #1085. Closes #1095. Closes #1096.
diff --git a/docs/versionhistory.rst b/docs/versionhistory.rst
@@ -20,6 +20,9 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 - Fixed the pytest plugin not running tests that had the ``anyio`` marker added
   programmatically via ``pytest_collection_modifyitems``
   (`#422 <https://github.com/agronholm/anyio/issues/422>`_; PR by @chbndrhnns)
+- Widened the type annotations of file I/O streams to accept ``IO[bytes]``
+  instead of just ``BinaryIO``
+  (`#1078 <https://github.com/agronholm/anyio/issues/1078>`_)
 
 **4.12.1**
 
diff --git a/src/anyio/streams/file.py b/src/anyio/streams/file.py
@@ -10,7 +10,7 @@
 from io import SEEK_SET, UnsupportedOperation
 from os import PathLike
 from pathlib import Path
-from typing import Any, BinaryIO, cast
+from typing import IO, Any
 
 from .. import (
     BrokenResourceError,
@@ -25,15 +25,15 @@
 
 class FileStreamAttribute(TypedAttributeSet):
     #: the open file descriptor
-    file: BinaryIO = typed_attribute()
+    file: IO[bytes] = typed_attribute()
     #: the path of the file on the file system, if available (file must be a real file)
     path: Path = typed_attribute()
     #: the file number, if available (file must be a real file or a TTY)
     fileno: int = typed_attribute()
 
 
 class _BaseFileStream:
-    def __init__(self, file: BinaryIO):
+    def __init__(self, file: IO[bytes]):
         self._file = file
 
     async def aclose(self) -> None:
@@ -76,7 +76,7 @@ async def from_path(cls, path: str | PathLike[str]) -> FileReadStream:
 
         """
         file = await to_thread.run_sync(Path(path).open, "rb")
-        return cls(cast(BinaryIO, file))
+        return cls(file)
 
     async def receive(self, max_bytes: int = 65536) -> bytes:
         try:
@@ -143,7 +143,7 @@ async def from_path(
         """
         mode = "ab" if append else "wb"
         file = await to_thread.run_sync(Path(path).open, mode)
-        return cls(cast(BinaryIO, file))
+        return cls(file)
 
     async def send(self, item: bytes) -> None:
         try:
