diff --git a/src/drf_yasg/openapi.py b/src/drf_yasg/openapi.py
index 5dc4b414..0a2cfb8f 100644
--- a/src/drf_yasg/openapi.py
+++ b/src/drf_yasg/openapi.py
@@ -2,8 +2,7 @@
 import logging
 import re
 import urllib.parse as urlparse
-from collections import OrderedDict
-from collections import abc as collections_abc
+from collections import OrderedDict, abc as collections_abc
 
 from django.urls import get_script_prefix
 from django.utils.functional import Promise
@@ -89,7 +88,7 @@ class SwaggerDict(OrderedDict):
     def __init__(self, **attrs):
         super(SwaggerDict, self).__init__()
         self._extras__ = attrs
-        if isinstance(self, SwaggerDict):
+        if type(self) == SwaggerDict:
             self._insert_extras__()
 
     def __setattr__(self, key, value):
@@ -517,7 +516,7 @@ def __init__(self, resolver, name, scope, expected_type, ignore_unresolved=False
         :param bool ignore_unresolved: do not throw if the referenced object does not exist
         """
         super(_Ref, self).__init__()
-        assert type(self) != _Ref, "do not instantiate _Ref directly"  # noqa: E721
+        assert not type(self) == _Ref, "do not instantiate _Ref directly"
         ref_name = "#/{scope}/{name}".format(scope=scope, name=name)
         if not ignore_unresolved:
             obj = resolver.get(name, scope)