PYTHONHOME is not absolutized

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-09-13.14:05:51.297>
labels = ['type-bug', '3.7']
title = 'PYTHONHOME is not absolutized'
updated_at = <Date 2017-09-13.14:05:51.297>
user = 'https://github.com/zhangyangyu'

bugs.python.org fields:

activity = <Date 2017-09-13.14:05:51.297>
actor = 'xiang.zhang'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2017-09-13.14:05:51.297>
creator = 'xiang.zhang'
dependencies = []
files = []
hgrepos = []
issue_num = 31451
keywords = []
message_count = 1.0
messages = ['302077']
nosy_count = 1.0
nosy_names = ['xiang.zhang']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31451'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7']