subclass meta mixins from type

This fixes a regression introduced in CPython 3.8.4.

Author: kam193

CHANGES.rst

@@ -1,3 +1,12 @@
+Version 2.4.4
+-------------
+
+Unreleased
+
+-   Change base class of meta mixins to ``type``. This fixes an issue
+    caused by a regression in CPython 3.8.4. :issue:`852`
+
+
 Version 2.4.3
 -------------
 

flask_sqlalchemy/model.py

@@ -59,7 +59,7 @@ def _join(match):
     return camelcase_re.sub(_join, name).lstrip('_')
 
 
-class NameMetaMixin(object):
+class NameMetaMixin(type):
     def __init__(cls, name, bases, d):
         if should_set_tablename(cls):
             cls.__tablename__ = camel_to_snake_case(cls.__name__)
@@ -111,7 +111,7 @@ def __table_cls__(cls, *args, **kwargs):
             del cls.__tablename__
 
 
-class BindMetaMixin(object):
+class BindMetaMixin(type):
     def __init__(cls, name, bases, d):
         bind_key = (
             d.pop('__bind_key__', None)