PYTHONHASHSEED=0 python3 -R should enable hash randomization

[vstinner]

BPO	32329
Nosy	@vstinner
PRs	bpo-32329: Fix -R option for hash randomization #4873 [3.6] bpo-32329: Fix sys.flags.hash_randomization #4875 bpo-32329: Add versionchanged to -R option doc #4884

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-12-15.15:41:41.471>
created_at = <Date 2017-12-14.23:11:19.999>
labels = ['3.7']
title = 'PYTHONHASHSEED=0 python3 -R should enable hash randomization'
updated_at = <Date 2017-12-15.15:41:41.470>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2017-12-15.15:41:41.470>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-12-15.15:41:41.471>
closer = 'vstinner'
components = []
creation = <Date 2017-12-14.23:11:19.999>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 32329
keywords = ['patch']
message_count = 5.0
messages = ['308343', '308348', '308354', '308355', '308405']
nosy_count = 1.0
nosy_names = ['vstinner']
pr_nums = ['4873', '4875', '4884']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue32329'
versions = ['Python 3.7']

[vstinner]

Python pretends that hash randomization is always enabled, but it's not:

$ PYTHONHASHSEED=0 python3 -c 'import sys; print(sys.flags.hash_randomization)'
1
vstinner@apu$ PYTHONHASHSEED=0 python3 -c 'import sys; print(hash("abc"))'
4596069200710135518
vstinner@apu$ PYTHONHASHSEED=0 python3 -c 'import sys; print(hash("abc"))'
4596069200710135518
vstinner@apu$ PYTHONHASHSEED=0 python3 -c 'import sys; print(hash("abc"))'
4596069200710135518

=> sys.flags.hash_randomization must be zero

Moreover, the -R flag is always ignored, it's not possible to override the PYTHONHASHSEED environment variable:

vstinner@apu$ PYTHONHASHSEED=0 python3 -R -c 'import sys; print(sys.flags.hash_randomization)'
1
vstinner@apu$ PYTHONHASHSEED=0 python3 -R -c 'import sys; print(hash("abc"))'
4596069200710135518
vstinner@apu$ PYTHONHASHSEED=0 python3 -R -c 'import sys; print(hash("abc"))'
4596069200710135518
vstinner@apu$ PYTHONHASHSEED=0 python3 -R -c 'import sys; print(hash("abc"))'
4596069200710135518

I expect that -R enables hash randomization and overrides PYTHONHASHSEED environment variable.

Attached PR fixes these issues and adds an unit test.

[vstinner]

New changeset 358e5e1 by Victor Stinner in branch 'master':
bpo-32329: Fix -R option for hash randomization (bpo-4873)
358e5e1

[vstinner]

New changeset 22097aa by Victor Stinner in branch '3.6':
bpo-32329: Fix sys.flags.hash_randomization (bpo-4875)
22097aa

[vstinner]

"PYTHONHASHSEED=0 python3 -R" now enables hash randomization on master (Python 3.7), I also fixed the sys.flags.hash_randomization value when using PYTHONHASHSEED=0.

I chose to not modify the behaviour of the -R option in Python 3.6. I dislike having to document a behaviour change in a minor Python version (3.6.x). I only fixed the value of sys.flags.hash_randomization in Python 3.6.

[vstinner]

New changeset 642d67b by Victor Stinner in branch 'master':
bpo-32329: Add versionchanged to -R option doc (bpo-4884)
642d67b