Deprecate the optional *random* argument to random.shuffle()

[rhettinger]

BPO	40465
Nosy	@tim-one, @rhettinger, @vstinner, @serhiy-storchaka, @hugovk
PRs	bpo-40465: Deprecate the optional argument to random.shuffle(). #19867 bpo-40465: Remove random module features deprecated in 3.9 #25874 bpo-40465: Document random module changes in 3.11 What's new #31818

^{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 2020-05-02.23:49:03.587>
created_at = <Date 2020-05-01.08:31:41.792>
labels = ['type-bug', 'library', '3.9']
title = 'Deprecate the optional *random* argument to random.shuffle()'
updated_at = <Date 2022-03-24.13:29:22.965>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2022-03-24.13:29:22.965>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-05-02.23:49:03.587>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2020-05-01.08:31:41.792>
creator = 'rhettinger'
dependencies = []
files = []
hgrepos = []
issue_num = 40465
keywords = ['patch']
message_count = 8.0
messages = ['367826', '367828', '367948', '370417', '370418', '415418', '415940', '415941']
nosy_count = 5.0
nosy_names = ['tim.peters', 'rhettinger', 'vstinner', 'serhiy.storchaka', 'hugovk']
pr_nums = ['19867', '25874', '31818']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40465'
versions = ['Python 3.9']

[rhettinger]

shuffle(x, random=None) ⟼ shuffle(x)

AFAICT, no one ever uses the optional parameter, nor would they have a valid reason to do so. It is an ancient API oddity and is inconsistent with the other methods in the module. I've long been annoyed by it and would like to see it cleaned-up before I retire ;-)

https://docs.python.org/3/library/random.html#random.shuffle

[serhiy-storchaka]

+1

[rhettinger]

New changeset 190fac9 by Raymond Hettinger in branch 'master':
bpo-40465: Deprecate the optional argument to random.shuffle(). (bpo-19867)
190fac9

[asottile]

pre-commit uses this to do deterministic shuffling, please don't remove this

pre-commit/pre-commit#1479

[serhiy-storchaka]

Raymond, could you please add an entry in What's New?

[hugovk]

#75999 adds an entry to What's New in 3.11.

[serhiy-storchaka]

New changeset 12c0012 by Tomáš Hrnčiar in branch 'main':
bpo-40465: Document random module changes in 3.11 What's new (bpo-31818)
12c0012

[vstinner]

commit 70a071d
Author: Raymond Hettinger <rhettinger@users.noreply.github.com>
Date: Tue May 4 01:55:40 2021 -0700

bpo-40465: Remove random module features deprecated in 3.9 (GH-25874)

[shaperilio]

AFAICT, no one ever uses the optional parameter, nor would they have a valid reason to do so. It is an ancient API oddity and is inconsistent with the other methods in the module. I've long been annoyed by it and would like to see it cleaned-up before I retire ;-)

Wow, what a bold statement 🤣. We were using it. Hope you're enjoying retirement.

Can someone help me understand the motivation for this? I keep clicking on links trying to figure it out if there was a bug associated with this, but I'm not familiar with the issue tracking here.

[serhiy-storchaka]

1. It complicated the code.
2. When that argument was specified, the result was less random.
3. The design just looked wrong.

[tim-one]

The default implementation of shuffle() stopped using random() long ago - it switched to a method avoiding floats entirely, and also avoiding the slight statistical biases the come with using floats for this.

So if you passed random= after that change, it went back to using the older - different & inherently biased - algorithm.

Keeping a worse algorithm in the code base was a Bad Idea on the face of it, especially given that nobody looking at this knew of anyone actually using the optional argument.

In the very early days, Python used the feeble (by current standards) Wichmann–Hill generator. Then there was far more user interest in replacing it with something better, even if slower. For the far fewer users who still care about that, there's a documented way to subclass Random now to use whatever other underlying generator you like better, and in a way that affects all the methods (not just shuffle()) building on the underlying generator.