python -m doctest script_file_with_no_py_extension produces confusing NameErrors

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-07-04.09:54:32.595>
labels = ['type-bug', 'library']
title = 'python -m doctest script_file_with_no_py_extension produces confusing NameErrors'
updated_at = <Date 2016-07-04.17:12:00.973>
user = 'https://bugs.python.org/towb'

bugs.python.org fields:

activity = <Date 2016-07-04.17:12:00.973>
actor = 'towb'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2016-07-04.09:54:32.595>
creator = 'towb'
dependencies = []
files = []
hgrepos = []
issue_num = 27447
keywords = []
message_count = 3.0
messages = ['269781', '269790', '269799']
nosy_count = 2.0
nosy_names = ['r.david.murray', 'towb']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27447'
versions = ['Python 3.6']