Slightly revised version of patch #1538956:

Replace UnicodeDecodeErrors raised during == and !=
compares of Unicode and other objects with a new
UnicodeWarning.

All other comparisons continue to raise exceptions.
Exceptions other than UnicodeDecodeErrors are also left
untouched.

Objects/exceptions.c

@@ -1948,6 +1948,14 @@ SimpleExtendsException(PyExc_Warning, ImportWarning,
           "Base class for warnings about probable mistakes in module imports");
 
 
+/*
+ *    UnicodeWarning extends Warning
+ */
+SimpleExtendsException(PyExc_Warning, UnicodeWarning,
+    "Base class for warnings about Unicode related problems, mostly\n"
+    "related to conversion problems.");
+
+
 /* Pre-computed MemoryError instance.  Best to create this as early as
  * possible and not wait until a MemoryError is actually raised!
  */
@@ -2048,6 +2056,7 @@ _PyExc_Init(void)
     PRE_INIT(RuntimeWarning)
     PRE_INIT(FutureWarning)
     PRE_INIT(ImportWarning)
+    PRE_INIT(UnicodeWarning)
 
     m = Py_InitModule4("exceptions", functions, exceptions_doc,
         (PyObject *)NULL, PYTHON_API_VERSION);
@@ -2113,6 +2122,7 @@ _PyExc_Init(void)
     POST_INIT(RuntimeWarning)
     POST_INIT(FutureWarning)
     POST_INIT(ImportWarning)
+    POST_INIT(UnicodeWarning)
 
     PyExc_MemoryErrorInst = BaseException_new(&_PyExc_MemoryError, NULL, NULL);
     if (!PyExc_MemoryErrorInst)