Title: Deprecate immortal interned strings: PyUnicode_InternImmortal()
Type: Stage: resolved
Components: Interpreter Core Versions: Python 3.10
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: Nosy List: corona10, methane, serhiy.storchaka, shihai1991, vstinner
Priority: normal Keywords: patch

Created on 2020-09-02 13:59 by vstinner, last changed 2021-05-10 04:20 by methane. This issue is now closed.

Pull Requests
URL Status Linked Edit
PR 22486 merged vstinner, 2020-10-01 22:58
Messages (8)
msg376237 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2020-09-02 13:59
Python has the concept of "immortal" interned strings: PyUnicode_InternImmortal().

The feature was first introduced in the Python 2 "str" (bytes) type, bpo-576101 (commit 45ec02aed14685c353e55841b5acbc0dadee76f8). New PyString_InternImmortal() function.

commit 45ec02aed14685c353e55841b5acbc0dadee76f8
Author: Guido van Rossum <>
Date:   Mon Aug 19 21:43:18 2002 +0000

    SF patch 576101, by Oren Tirosh: alternative implementation of
    interning.  I modified Oren's patch significantly, but the basic idea
    and most of the implementation is unchanged.  Interned strings created
    with PyString_InternInPlace() are now mortal, and you must keep a
    reference to the resulting string around; use the new function
    PyString_InternImmortal() to create immortal interned strings.

Later, the feature was added to the PyUnicodeObject type, new PyUnicode_InternImmortal() function:

commit 1680713e524016d93a94114c4a874ad71a090b95
Author: Walter Dörwald <>
Date:   Fri May 25 13:52:07 2007 +0000

    Add interning of unicode strings by copying the functionality from
    Intern "True" and "False" in bool_repr() again as it was in the
    8bit string era.

Since Python 3.10, (mortal) interned strings are cleared at Python exit in Py_Finalize(). It avoids leaking memory when Python is embedded in an application: bpo-1635741.

commit 666ecfb0957a2fa0df5e2bd03804195de74bdfbf
Author: Victor Stinner <>
Date:   Thu Jul 2 01:19:57 2020 +0200

    bpo-1635741: Release Unicode interned strings at exit (GH-21269)
    * PyUnicode_InternInPlace() now ensures that interned strings are
    * Add _PyUnicode_ClearInterned().
    * Py_Finalize() now releases Unicode interned strings:
      call _PyUnicode_ClearInterned().


PyUnicode_InternImmortal() is not used in the Python standard library. I propose to start deprecating the function and remove it in Python 3.12 (PEP 387 requires a deprecation for 2 releases). In Python 3.10, calling the function will emit a DeprecationWarning at runtime.

Note: PyString_InternImmortal() (for bytes strings) has been removed from Python 3.0.
msg376271 - (view) Author: Inada Naoki (methane) * (Python committer) Date: 2020-09-03 01:19
msg376302 - (view) Author: Dong-hee Na (corona10) * (Python committer) Date: 2020-09-03 14:19
msg376428 - (view) Author: Hai Shi (shihai1991) * (Python triager) Date: 2020-09-05 10:40
msg377784 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2020-10-01 23:00
I proposed PR 22486 to deprecate the function.
msg377808 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2020-10-02 12:49
New changeset 583ee5a5b1971a18ebeb877948ce6264da0cc8aa by Victor Stinner in branch 'master':
bpo-41692: Deprecate PyUnicode_InternImmortal() (GH-22486)
msg377809 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2020-10-02 12:49
The function is now deprecated. Thanks for the review INADA-san, I close the issue. Let's meet in Python 3.12 to remove it ;-)
msg393350 - (view) Author: Inada Naoki (methane) * (Python committer) Date: 2021-05-10 04:20
For the record, I noticed PyUnicode_InternImmortal() is a stable ABI.

We may need to keep the function to avoid dynamic link errors.
But we can still change its implementation to just raise an exception.
Date User Action Args
2021-05-10 04:20:28methanesetmessages: + msg393350
2020-10-02 12:49:46vstinnersetstatus: open -> closed
resolution: fixed
messages: + msg377809

stage: patch review -> resolved
2020-10-02 12:49:08vstinnersetmessages: + msg377808
2020-10-01 23:00:06vstinnersetmessages: + msg377784
2020-10-01 22:58:56vstinnersetkeywords: + patch
stage: patch review
pull_requests: + pull_request21503
2020-09-05 10:40:01shihai1991setmessages: + msg376428
2020-09-03 14:19:26corona10setmessages: + msg376302
2020-09-03 14:19:14corona10setnosy: + corona10
2020-09-03 01:19:36methanesetmessages: + msg376271
2020-09-02 16:02:12shihai1991setnosy: + shihai1991
2020-09-02 13:59:25vstinnercreate