--- a/cubicweb/web/schemaviewer.py	Fri Apr 05 17:21:14 2019 +0200
+++ b/cubicweb/web/schemaviewer.py	Fri Apr 05 17:58:19 2019 +0200
@@ -20,8 +20,6 @@
 
 from cubicweb import _
 
-from six import string_types
-
 from logilab.common.ureports import Section, Title, Table, Link, Span, Text
 
 from yams.schema2dot import CARD_MAP
@@ -228,7 +226,7 @@
                     elif isinstance(val, (list, tuple)):
                         val = sorted(val)
                         val = ', '.join(str(v) for v in val)
-                    elif val and isinstance(val, string_types):
+                    elif val and isinstance(val, str):
                         val = _(val)
                     else:
                         val = str(val)