Wrong ExitStack Callback recipe

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-11-27.08:34:13.573>
labels = ['type-bug', '3.7', 'docs']
title = 'Wrong ExitStack Callback recipe'
updated_at = <Date 2018-01-02.07:21:53.341>
user = 'https://github.com/Denaun'

bugs.python.org fields:

activity = <Date 2018-01-02.07:21:53.341>
actor = 'ncoghlan'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2017-11-27.08:34:13.573>
creator = 'Denaun'
dependencies = []
files = []
hgrepos = []
issue_num = 32145
keywords = []
message_count = 8.0
messages = ['307037', '307364', '308011', '309046', '309064', '309172', '309176', '309357']
nosy_count = 4.0
nosy_names = ['barry', 'ncoghlan', 'docs@python', 'Denaun']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32145'
versions = ['Python 3.6', 'Python 3.7']