Improve scope example in Tutorial, chapter 9

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-11-03.20:32:41.315>
labels = ['type-feature', '3.8', 'docs']
title = 'Improve scope example in Tutorial, chapter 9'
updated_at = <Date 2019-11-08.22:58:43.013>
user = 'https://bugs.python.org/DavidGoldsmith'

bugs.python.org fields:

activity = <Date 2019-11-08.22:58:43.013>
actor = 'terry.reedy'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2019-11-03.20:32:41.315>
creator = 'David Goldsmith'
dependencies = []
files = []
hgrepos = []
issue_num = 38675
keywords = []
message_count = 2.0
messages = ['355908', '356272']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'docs@python', 'David Goldsmith']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue38675'
versions = ['Python 3.8']