clarified assertion message

git-svn-id: http://svn.code.sf.net/p/docutils/code/trunk/docutils@3654 929543f6-e4f2-0310-98a6-ba3bd3dd1d04

1 files changed, 3 insertions, 1 deletions

diff --git a/docutils/io.py b/docutils/io.py
index 91b70377e..5a6672e15 100644
--- a/docutils/io.py
+++ b/docutils/io.py
@@ -149,7 +149,9 @@ class Output(TransformSpec):
 
     def encode(self, data):
         if self.encoding and self.encoding.lower() == 'unicode':
-            assert isinstance(data, UnicodeType), 'no unicode output'
+            assert isinstance(data, UnicodeType), (
+                'the encoding given is "unicode" but the output is not '
+                'a Unicode string')
             return data
         if not isinstance(data, UnicodeType):
             # Non-unicode (e.g. binary) output.