Octal byte literals with a decimal value > 255 are silently truncated

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-09-10.11:57:43.411>
labels = ['interpreter-core', 'type-bug', '3.7', 'OS-windows']
title = 'Octal byte literals with a decimal value > 255 are silently truncated'
updated_at = <Date 2018-09-10.11:57:43.411>
user = 'https://github.com/mr-nfamous'

bugs.python.org fields:

activity = <Date 2018-09-10.11:57:43.411>
actor = 'bup'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core', 'Windows']
creation = <Date 2018-09-10.11:57:43.411>
creator = 'bup'
dependencies = []
files = []
hgrepos = []
issue_num = 34620
keywords = []
message_count = 1.0
messages = ['324918']
nosy_count = 5.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'steve.dower', 'bup']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34620'
versions = ['Python 3.6', 'Python 3.7']