A string representation of slice objects with colon syntax

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-11-13.18:47:56.222>
labels = ['interpreter-core', 'type-feature', '3.10']
title = 'A string representation of slice objects with colon syntax'
updated_at = <Date 2020-11-21.01:37:45.688>
user = 'https://github.com/rossbar'

bugs.python.org fields:

activity = <Date 2020-11-21.01:37:45.688>
actor = 'terry.reedy'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2020-11-13.18:47:56.222>
creator = 'rossbar'
dependencies = []
files = []
hgrepos = []
issue_num = 42352
keywords = []
message_count = 2.0
messages = ['380921', '381516']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'rossbar']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue42352'
versions = ['Python 3.10']