allow to use sets in field choices (#1482)

docs/changelog.rst

@@ -4,7 +4,8 @@ Changelog
 
 Development
 ===========
-- (Fill this out as you fix issues and develop you features).
+- (Fill this out as you fix issues and develop your features).
+- Fixed using sets in field choices #1481
 - POTENTIAL BREAKING CHANGE: Fixed limit/skip/hint/batch_size chaining #1476
 - POTENTIAL BREAKING CHANGE: Changed a public `QuerySet.clone_into` method to a private `QuerySet._clone_into` #1476
 - Fixed connecting to a replica set with PyMongo 2.x #1436

docs/guide/defining-documents.rst

@@ -150,7 +150,7 @@ arguments can be set on all fields:
     .. note:: If set, this field is also accessible through the `pk` field.
 
 :attr:`choices` (Default: None)
-    An iterable (e.g. a list or tuple) of choices to which the value of this
+    An iterable (e.g. list, tuple or set) of choices to which the value of this
     field should be limited.
 
     Can be either be a nested tuples of value (stored in mongo) and a
@@ -214,8 +214,8 @@ document class as the first argument::
 
 Dictionary Fields
 -----------------
-Often, an embedded document may be used instead of a dictionary – generally 
-embedded documents are recommended as dictionaries don’t support validation 
+Often, an embedded document may be used instead of a dictionary – generally
+embedded documents are recommended as dictionaries don’t support validation
 or custom field types. However, sometimes you will not know the structure of what you want to
 store; in this situation a :class:`~mongoengine.fields.DictField` is appropriate::