Remove support for string exceptions.

They have been removed in Python 2.6. In case of a string raised, it will end up as a `InvalidErrorTypeExpression`.

CHANGES.rst

@@ -9,6 +9,9 @@ Changelog
 
 - Added support for Python 3.7.
 
+- Remove support for string exceptions in ``<dtml-except>``.
+
+
 3.0b4 (2018-07-12)
 ------------------
 

src/DocumentTemplate/DT_Try.py

@@ -154,10 +154,7 @@ def render_try_except(self, md):
         except Exception:
             # but an error occurs.. save the info.
             t, v = sys.exc_info()[:2]
-            if isinstance(t, str):
-                errname = t
-            else:
-                errname = t.__name__
+            errname = t.__name__
 
             handler = self.find_handler(t)
 
@@ -196,12 +193,6 @@ def render_try_finally(self, md):
 
     def find_handler(self, exception):
         "recursively search for a handler for a given exception"
-        if isinstance(exception, str):
-            for e, h in self.handlers:
-                if exception == e or e == '':
-                    return h
-            else:
-                return None
         for e, h in self.handlers:
             if (e == exception.__name__ or
                     e == '' or self.match_base(exception, e)):