urllib.request.Request accepts but doesn't check bytes headers

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-03-23.22:03:56.696>
labels = ['3.7', 'type-bug', 'library']
title = "urllib.request.Request accepts but doesn't check bytes headers"
updated_at = <Date 2017-03-25.01:01:46.654>
user = 'https://github.com/ezio-melotti'

bugs.python.org fields:

activity = <Date 2017-03-25.01:01:46.654>
actor = 'martin.panter'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-03-23.22:03:56.696>
creator = 'ezio.melotti'
dependencies = []
files = []
hgrepos = []
issue_num = 29891
keywords = []
message_count = 2.0
messages = ['290063', '290457']
nosy_count = 4.0
nosy_names = ['orsenthil', 'ezio.melotti', 'martin.panter', 'maciej.szulik']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29891'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']