bpo-43680: Deprecate io.OpenWrapper (GH-25357)

Deprecate io.OpenWrapper and _pyio.OpenWrapper: use io.open and
_pyio.open instead. Until Python 3.9, _pyio.open was not a static
method and builtins.open was set to OpenWrapper to not become a bound
method when set to a class variable. _io.open is a built-in function
whereas _pyio.open is a Python function. In Python 3.10, _pyio.open()
is now a static method, and builtins.open() is now io.open().

1 files changed, 16 insertions, 1 deletions

diff --git a/Lib/io.py b/Lib/io.py
index 01f1df80ded..2a6140c3dd5 100644
--- a/Lib/io.py
+++ b/Lib/io.py
@@ -56,7 +56,22 @@ from _io import (DEFAULT_BUFFER_SIZE, BlockingIOError, UnsupportedOperation,
                  BufferedWriter, BufferedRWPair, BufferedRandom,
                  IncrementalNewlineDecoder, text_encoding, TextIOWrapper)
 
-OpenWrapper = _io.open # for compatibility with _pyio
+
+def __getattr__(name):
+    if name == "OpenWrapper":
+        # bpo-43680: Until Python 3.9, _pyio.open was not a static method and
+        # builtins.open was set to OpenWrapper to not become a bound method
+        # when set to a class variable. _io.open is a built-in function whereas
+        # _pyio.open is a Python function. In Python 3.10, _pyio.open() is now
+        # a static method, and builtins.open() is now io.open().
+        import warnings
+        warnings.warn('OpenWrapper is deprecated, use open instead',
+                      DeprecationWarning, stacklevel=2)
+        global OpenWrapper
+        OpenWrapper = open
+        return OpenWrapper
+    raise AttributeError(name)
+
 
 # Pretend this exception was created here.
 UnsupportedOperation.__module__ = "io"