Let to_unicode be more graceful for non-unicode strings, as like CMFPlone's

safe_unicode does it.

CHANGES.rst

@@ -2,6 +2,14 @@
 Changelog
 =========
 
+3.5dev (unreleased)
+-------------------
+
+- Let to_unicode be more graceful for non-unicode strings, as like CMFPlone's
+  safe_unicode does it.
+  [thet]
+
+
 3.4 (2013-04-24)
 ----------------
 

src/icalendar/parser_tools.py

@@ -7,12 +7,12 @@ def to_unicode(value, encoding='utf-8'):
     """
     if isinstance(value, unicode):
         return value
-    elif isinstance(value, str):
+    elif isinstance(value, basestring):
         try:
-            return value.decode(encoding)
-        except UnicodeDecodeError:
-            return value.decode('utf-8', 'replace')
-    raise AssertionError('A str/unicode expected.')
+            value = unicode(value, encoding)
+        except (UnicodeDecodeError):
+            value = value.decode('utf-8', 'replace')
+    return value
 
 
 def data_encode(data, encoding=DEFAULT_ENCODING):

src/icalendar/tests/test_unit_parser_tools.py

@@ -15,10 +15,8 @@ class TestParserTools(unittest.TestCase):
         self.assertEqual(to_unicode(u'\xc6\xb5'.encode('iso-8859-1')),
                          u'\u01b5')
         self.assertEqual(to_unicode('\xc6\xb5', encoding='ascii'), u'\u01b5')
-        with self.assertRaises(AssertionError):
-            to_unicode(1)
-        with self.assertRaises(AssertionError):
-            to_unicode(None)
+        self.assertEqual(to_unicode(1), 1)
+        self.assertEqual(to_unicode(None), None)
 
     def test_parser_tools_data_encode(self):