Add sys.isinterned()

[serhiy-storchaka]

BPO	34392
Nosy	@warsaw, @brettcannon, @rhettinger, @ronaldoussoren, @tiran, @serhiy-storchaka
PRs	bpo-34392: Add sys. _is_interned() #8755

^{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 2018-08-13.10:24:33.256>
labels = ['interpreter-core', 'type-feature', '3.8']
title = 'Add sys.isinterned()'
updated_at = <Date 2018-08-19.06:55:15.282>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2018-08-19.06:55:15.282>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2018-08-13.10:24:33.256>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 34392
keywords = ['patch']
message_count = 5.0
messages = ['323473', '323474', '323539', '323545', '323744']
nosy_count = 6.0
nosy_names = ['barry', 'brett.cannon', 'rhettinger', 'ronaldoussoren', 'christian.heimes', 'serhiy.storchaka']
pr_nums = ['8755']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue34392'
versions = ['Python 3.8']

[serhiy-storchaka]

I need to test whether the string is interned for Python implementations of marshal.dumps(). It is easy to do in C, and I suggest to expose this functionality to Python.

Currently you can test if the string is interned using the following function:

    def isinterned(s):
        return sys.intern(s) is s

But it has a side effect -- it interns a string if it is not equal to an already interned string.

[tiran]

I'd prefer to have this as an internal API, either sys._isinterned() or as a helper method in testcapi.

[brettcannon]

I agree with Christian; this is an implementation detail so it should be flagged as private/internal somehow.

[warsaw]

Agreed it should be non-public, but can we please call it sys._is_interned()?

[serhiy-storchaka]

Thank you all for the feedback. The function is renamed to sys._is_interned() and documented as optional.