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, 14 insertions, 12 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index cb5a619..56e9a0c 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -311,18 +311,20 @@ except AttributeError:
     open_code = _open_code_with_warning
 
 
-class DocDescriptor:
-    """Helper for builtins.open.__doc__
-    """
-    def __get__(self, obj, typ=None):
-        return (
-            "open(file, mode='r', buffering=-1, encoding=None, "
-                 "errors=None, newline=None, closefd=True)\n\n" +
-            open.__doc__)
-
-
-# bpo-43680: Alias to open() kept for backward compatibility
-OpenWrapper = open
+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)
 
 
 # In normal operation, both `UnsupportedOperation`s should be bound to the