SF patch #1056967, changes the semantics of Template.safe_substitute() to not

raise a ValueError for dangling delimiters (the delimiter itself is returned).

Lib/string.py

@@ -199,7 +199,7 @@ class Template:
             if mo.group('escaped') is not None:
                 return self.delimiter
             if mo.group('invalid') is not None:
-                self._invalid(mo)
+                return self.delimiter
             raise ValueError('Unrecognized named group in pattern',
                              self.pattern)
         return self.pattern.sub(convert, self.template)