Fix linting issues.

src/drf_yasg/inspectors/field.py

@@ -189,7 +189,7 @@ def get_queryset_from_view(view, serializer=None):
 
         if queryset is not None and serializer is not None:
             # make sure the view is actually using *this* serializer
-            assert type(serializer) == call_view_method(view, 'get_serializer_class', 'serializer_class')
+            assert type(serializer) is call_view_method(view, 'get_serializer_class', 'serializer_class')
 
         return queryset
     except Exception:  # pragma: no cover

src/drf_yasg/openapi.py

@@ -88,7 +88,7 @@ class SwaggerDict(OrderedDict):
     def __init__(self, **attrs):
         super(SwaggerDict, self).__init__()
         self._extras__ = attrs
-        if type(self) == SwaggerDict:
+        if type(self) is SwaggerDict:
             self._insert_extras__()
 
     def __setattr__(self, key, value):
@@ -516,7 +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 not type(self) == _Ref, "do not instantiate _Ref directly"
+        assert type(self) is not _Ref, "do not instantiate _Ref directly"
         ref_name = "#/{scope}/{name}".format(scope=scope, name=name)
         if not ignore_unresolved:
             obj = resolver.get(name, scope)

src/drf_yasg/utils.py

@@ -442,7 +442,7 @@ def force_real_str(s, encoding='utf-8', strings_only=False, errors='strict'):
     """
     if s is not None:
         s = force_str(s, encoding, strings_only, errors)
-        if type(s) != str:
+        if type(s) is not str:  # noqa: E721
             s = '' + s
 
         # Remove common indentation to get the correct Markdown rendering