Fixed #21198 -- Prevented invalid use of @python_2_unicode_compatible.

Thanks jpic for the report and chmodas for working on a patch.

Reverts 2ea80b94. Refs #19362.

Conflicts:
	tests/utils_tests/test_encoding.py

1 files changed, 4 insertions, 0 deletions

diff --git a/django/utils/encoding.py b/django/utils/encoding.py
index ad06336c4d..599952bdeb 100644
--- a/django/utils/encoding.py
+++ b/django/utils/encoding.py
@@ -52,6 +52,10 @@ def python_2_unicode_compatible(klass):
     returning text and apply this decorator to the class.
     """
     if six.PY2:
+        if '__str__' not in klass.__dict__:
+            raise ValueError("@python_2_unicode_compatible cannot be applied "
+                             "to %s because it doesn't define __str__()." %
+                             klass.__name__)
         klass.__unicode__ = klass.__str__
         klass.__str__ = lambda self: self.__unicode__().encode('utf-8')
     return klass