Deprecate shlex.split(None) to read from stdin.

[tiran]

BPO	33262
Nosy	@ericvsmith, @tiran, @pganssle, @ZackerySpytz, @NiklasRosenstein, @akulakov
PRs	bpo-33262: Deprecate passing None for s to shlex.split() #6514

^{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 2018-04-11.10:28:49.441>
labels = ['3.8', 'type-bug', 'library']
title = 'Deprecate shlex.split(None) to read from stdin.'
updated_at = <Date 2021-08-29.19:19:42.031>
user = 'https://github.com/tiran'

bugs.python.org fields:

activity = <Date 2021-08-29.19:19:42.031>
actor = 'andrei.avk'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2018-04-11.10:28:49.441>
creator = 'christian.heimes'
dependencies = []
files = []
hgrepos = []
issue_num = 33262
keywords = ['patch']
message_count = 5.0
messages = ['315189', '315209', '323489', '365468', '400555']
nosy_count = 6.0
nosy_names = ['eric.smith', 'christian.heimes', 'p-ganssle', 'ZackerySpytz', 'n_rosenstein', 'andrei.avk']
pr_nums = ['6514']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33262'
versions = ['Python 3.8']

[tiran]

The shlex module implements simple tokenize for a shell-like mini language. The shlex.split() function splits a string into subcomponents just like a typical Unix shell. However function has a surprising feature. When None is passed into shlex.split().

Note: Since the split() function instantiates a shlex instance, passing None for s will read the string to split from standard input.

https://docs.python.org/3/library/shlex.html#shlex.split

This is both surprising, unnecessary and potentially dangerous. Reading from sys.stdin is a blocking operation. In case an application doesn't account for None, shlex.split(value) could lead to a blocked server application. I suggest to deprecate and eventually remove this mis-feature.

Credits: David R. MacIver reported the bug on Twitter: https://twitter.com/DRMacIver/status/984001867985367040

[ericvsmith]

I agree that it should be deprecated. That's crazy behavior.

I'd also recommend that shlex.shlex with instream=None be deprecated, but maybe that's too radical. It seems way too easy to accidentally pass in None.

[NiklasRosenstein]

I've just run into this as well -- I thought it was a bug until I found this issue. I also think that this is anything from sane.

[pganssle]

New changeset 975ac32 by Zackery Spytz in branch 'master':
bpo-33262: Deprecate passing None for s to shlex.split() (GH-6514)
975ac32

[akulakov]

Can be closed as fixed (or perhaps renamed and kept open to track eventual raising of error in the future?)

[vstinner]

Follow-up issue #94352: shlex.split(): remove support for s=None.