fix from code review regarding py2py3 compat

CONTRIBUTING.rst

@@ -28,8 +28,8 @@ Python 2/3 compatibility
 
 The codebase is written in a compatible manner for python 2 & 3 so it
 is important that this is taken into account when it comes to discrepencies
-between the 2 versions (check this https://python-future.org/compatible_idioms.html).
-Travis runs run the tests against the different versions as a safety net.
+between the two versions (see https://python-future.org/compatible_idioms.html).
+Travis runs the tests against different Python versions as a safety net.
 
 
 Style Guide

mongoengine/base/datastructures.py

@@ -1,6 +1,7 @@
 import weakref
 
 from bson import DBRef
+from future.utils import listitems
 import six
 from six import iteritems
 
@@ -422,10 +423,10 @@ class StrictDict(object):
         return len(list(iteritems(self)))
 
     def __eq__(self, other):
-        return list(self.items()) == list(other.items())
+        return listitems(self) == listitems(other)
 
     def __ne__(self, other):
-        return list(self.items()) != list(other.items())
+        return not(self == other)
 
     @classmethod
     def create(cls, allowed_keys):

tests/fields/test_sequence_field.py

@@ -267,12 +267,12 @@ class TestSequenceField(MongoDBTestCase):
         foo = Foo(name="Foo")
         foo.save()
 
-        assert not (
-            "base.counter" in self.db["mongoengine.counters"].find().distinct("_id")
+        assert (
+            "base.counter" not in self.db["mongoengine.counters"].find().distinct("_id")
         )
-        assert ("foo.counter" and "bar.counter") in self.db[
-            "mongoengine.counters"
-        ].find().distinct("_id")
+        existing_counters = self.db["mongoengine.counters"].find().distinct("_id")
+        assert "foo.counter" in existing_counters
+        assert "bar.counter" in existing_counters
         assert foo.counter == bar.counter
         assert foo._fields["counter"].owner_document == Foo
         assert bar._fields["counter"].owner_document == Bar