python -h dosen't list -R option

[180909]

BPO	45742
Nosy	@terryjreedy, @vstinner, @eryksun

^{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 = None
created_at = <Date 2021-11-07.03:10:01.137>
labels = ['3.11', '3.9', '3.10', 'docs']
title = "python -h can't  find -R option"
updated_at = <Date 2021-11-14.17:23:34.386>
user = 'https://github.com/180909'

bugs.python.org fields:

activity = <Date 2021-11-14.17:23:34.386>
actor = 'terry.reedy'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2021-11-07.03:10:01.137>
creator = 'wangjiahua'
dependencies = []
files = []
hgrepos = []
issue_num = 45742
keywords = []
message_count = 9.0
messages = ['405891', '405903', '405904', '406239', '406254', '406259', '406315', '406316', '406326']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'vstinner', 'docs@python', 'eryksun']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue45742'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

Linked PRs

• gh-89905: Correct -R option doc #137608

[180909]

I input python -h on the command line, and I can't find any -R option.

[eryksun]

Apparently -R is still implemented in Python 3, even though hash randomization is enabled by default now. Unlike Python 2, in Python 3 -R overrides the PYTHONHASHSEED environment variable, making it effectively the same as "PYTHONHASHSEED=random". For example:

Python 2.7.18

    $ PYTHONHASHSEED=37 python2
    >>> import sys; sys.flags.hash_randomization
    37
    >>> hash('spam')
    -3063226141675644153

    $ PYTHONHASHSEED=37 python2 -R
    >>> import sys; sys.flags.hash_randomization
    37
    >>> hash('spam')
    -3063226141675644153

Python 3.11

    $ PYTHONHASHSEED=37 python3 -q
    >>> import sys; sys.flags.hash_randomization
    1
    >>> hash('spam')
    7085596773562191897

    $ PYTHONHASHSEED=37 python3 -q
    >>> hash('spam')
    7085596773562191897

    $ PYTHONHASHSEED=37 python3 -qR
    >>> import sys; sys.flags.hash_randomization
    1
    >>> hash('spam')
    -6544739063919843911

    $ PYTHONHASHSEED=37 python3 -qR
    >>> hash('spam')
    5363435507110042548

Python 3 no longer reports the seed value in sys.flags.hash_randomization, so I repeated the 3.11 examples twice to show that PYTHONHASHSEED works, except when -R overrides it.

[eryksun]

Either the documentation [1] or the behavior needs to be fixed. The following statement is false:

Turn on hash randomization. This option only has an effect if the
PYTHONHASHSEED environment variable is set to 0, since hash
randomization is enabled by default.

---
[1] https://docs.python.org/3.10/using/cmdline.html#cmdoption-R

[terryjreedy]

Victor, A sentence about hash randomization you wrote for bpo-32329 in PR-4873 is not currently correct. Change code or doc?

[vstinner]

I input python -h on the command line, and I can't find any -R option.

If you want to document it, the "usage" is in Python/initconfig.c. See also the -R option. My notes on adding a command line option:
https://pythondev.readthedocs.io/pyconfig.html#add-a-new-command-line-option

Victor, A sentence about hash randomization you wrote for bpo-32329 in PR-4873 is not currently correct. Change code or doc?

In Python/initconfig.c, the -R option sets config->use_hash_seed to 0. It overrides PYTHONHASHSEED env var, as documented at:
https://docs.python.org/3.10/using/cmdline.html#cmdoption-R

IMO it's the expected behavior. Cmd line must have the priority over env vars.

Which doc is wrong?