From f71ef68a55efcc5bbe6ece9e0a19f7bf7e3495b5 Mon Sep 17 00:00:00 2001
From: pacocartones <manusanchezhl@gmail.com>
Date: Thu, 13 Aug 2026 05:10:44 +0200
Subject: [PATCH] [subprocess] Restore `IO[AnyStr]` on `Popen` stream
 attributes

`Popen` is generic in `AnyStr`, but `stdin`, `stdout` and `stderr` were
annotated as `IO[Any]`, which dropped the type parameter. Restore
`IO[AnyStr]` and add a regression test case.
---
 stdlib/@tests/test_cases/check_subprocess.py | 40 ++++++++++++++++++++
 stdlib/subprocess.pyi                        |  6 +--
 2 files changed, 43 insertions(+), 3 deletions(-)
 create mode 100644 stdlib/@tests/test_cases/check_subprocess.py

diff --git a/stdlib/@tests/test_cases/check_subprocess.py b/stdlib/@tests/test_cases/check_subprocess.py
new file mode 100644
index 000000000000..4d599ecb51cd
--- /dev/null
+++ b/stdlib/@tests/test_cases/check_subprocess.py
@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+from subprocess import PIPE, Popen
+from typing import IO
+from typing_extensions import assert_type
+
+
+def check_streams_follow_the_type_parameter() -> None:
+    # Popen is generic in AnyStr, and the std* streams must carry that
+    # parameter through instead of degrading to IO[Any].
+    with Popen(["command"], stdin=PIPE, stdout=PIPE, stderr=PIPE) as process:
+        assert_type(process, Popen[bytes])
+        assert_type(process.stdin, IO[bytes] | None)
+        assert_type(process.stdout, IO[bytes] | None)
+        assert_type(process.stderr, IO[bytes] | None)
+
+    with Popen(["command"], stdin=PIPE, stdout=PIPE, stderr=PIPE, text=True) as process_text:
+        assert_type(process_text, Popen[str])
+        assert_type(process_text.stdin, IO[str] | None)
+        assert_type(process_text.stdout, IO[str] | None)
+        assert_type(process_text.stderr, IO[str] | None)
+
+
+def check_streams_follow_the_other_text_arguments() -> None:
+    with Popen(["command"], stdout=PIPE, encoding="utf-8") as process_encoding:
+        assert_type(process_encoding.stdout, IO[str] | None)
+
+    with Popen(["command"], stdout=PIPE, errors="replace") as process_errors:
+        assert_type(process_errors.stdout, IO[str] | None)
+
+    with Popen(["command"], stdout=PIPE, universal_newlines=True) as process_universal:
+        assert_type(process_universal.stdout, IO[str] | None)
+
+
+def check_reading_a_stream_yields_the_right_type() -> None:
+    with Popen(["command"], stdout=PIPE, text=True) as process:
+        if process.stdout is not None:
+            assert_type(process.stdout.read(), str)
+            for line in process.stdout:
+                assert_type(line, str)
diff --git a/stdlib/subprocess.pyi b/stdlib/subprocess.pyi
index c191f0e35de9..0790069c115c 100644
--- a/stdlib/subprocess.pyi
+++ b/stdlib/subprocess.pyi
@@ -1030,9 +1030,9 @@ class CalledProcessError(SubprocessError):
 
 class Popen(Generic[AnyStr]):
     args: _CMD
-    stdin: IO[Any] | None
-    stdout: IO[Any] | None
-    stderr: IO[Any] | None
+    stdin: IO[AnyStr] | None
+    stdout: IO[AnyStr] | None
+    stderr: IO[AnyStr] | None
     pid: int
     returncode: int | MaybeNone
     universal_newlines: bool