gh-78889: Stop IDLE Shell freezes from sys.stdout.shell.xyz (#121876)

Problem occurred when attribute xyz could not be pickled.
Since this is not trivial to selectively fix, block all
attributes (other than 'width').  IDLE does not access them
and they are private implementation details.

Lib/idlelib/News3.txt

@@ -4,6 +4,9 @@ Released on 2024-10-xx
 =========================
 
 
+gh-78889: Stop Shell freezes by blocking user access to non-method
+sys.stdout.shell attributes, which are all private.
+
 gh-78955: Use user-selected color theme for Help => IDLE Doc.
 
 gh-96905: In idlelib code, stop redefining built-ins 'dict' and 'object'.

Lib/idlelib/run.py

@@ -443,6 +443,9 @@ class StdioFile(io.TextIOBase):
 
     def __init__(self, shell, tags, encoding='utf-8', errors='strict'):
         self.shell = shell
+        # GH-78889: accessing unpickleable attributes freezes Shell.
+        # IDLE only needs methods; allow 'width' for possible use.
+        self.shell._RPCProxy__attributes = {'width': 1}
         self.tags = tags
         self._encoding = encoding
         self._errors = errors

Misc/NEWS.d/next/IDLE/2024-07-16-16-57-03.gh-issue-78889.U7ghFD.rst

@@ -0,0 +1,2 @@
+Stop Shell freezes by blocking user access to non-method sys.stdout.shell attributes,
+which are all private.