Abstract instance and class attributes for abstract base classes

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-08-12.23:48:29.010>
labels = ['type-feature', '3.9']
title = 'Abstract instance and class attributes for abstract base classes'
updated_at = <Date 2021-08-16.11:39:37.461>
user = 'https://bugs.python.org/rzepeckit'

bugs.python.org fields:

activity = <Date 2021-08-16.11:39:37.461>
actor = 'ajoino'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-08-12.23:48:29.010>
creator = 'rzepecki.t'
dependencies = []
files = ['50213']
hgrepos = []
issue_num = 44905
keywords = []
message_count = 5.0
messages = ['399486', '399534', '399649', '399650', '399653']
nosy_count = 3.0
nosy_names = ['ajoino', 'AlexWaygood', 'rzepecki.t']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44905'
versions = ['Python 3.9']