revert more that would affect pickling

Author: JelleZijlstra

Lib/dataclasses.py

@@ -172,7 +172,10 @@ class FrozenInstanceError(AttributeError): pass
 # A sentinel object for default values to signal that a default
 # factory will be used.  This is given a nice repr() which will appear
 # in the function signature of dataclasses' constructors.
-_HAS_DEFAULT_FACTORY = sentinel('<factory>')
+class _HAS_DEFAULT_FACTORY_CLASS:
+    def __repr__(self):
+        return '<factory>'
+_HAS_DEFAULT_FACTORY = _HAS_DEFAULT_FACTORY_CLASS()
 
 # A sentinel object to detect if a parameter is supplied or not.
 MISSING = sentinel("MISSING")

Lib/traceback.py

@@ -136,7 +136,11 @@ def extract_tb(tb, limit=None):
     "another exception occurred:\n\n")
 
 
-_sentinel = sentinel("<implicit>")
+class _Sentinel:
+    def __repr__(self):
+        return "<implicit>"
+
+_sentinel = _Sentinel()
 
 def _parse_value_tb(exc, value, tb):
     if (value is _sentinel) != (tb is _sentinel):