Align io.py more squarely with CPython 3.10

Author: fanninpm

Lib/io.py

@@ -55,15 +55,29 @@
                  open, open_code, BytesIO, StringIO, BufferedReader,
                  BufferedWriter, BufferedRWPair, BufferedRandom,
                  # XXX RUSTPYTHON TODO: IncrementalNewlineDecoder
-                 # IncrementalNewlineDecoder, TextIOWrapper)
-                 TextIOWrapper)
+                 # IncrementalNewlineDecoder, text_encoding, TextIOWrapper)
+                 text_encoding, TextIOWrapper)
 
 try:
     from _io import FileIO
 except ImportError:
     pass
 
-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"