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 <guido@python.org>
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 <walter@livinglogic.de>
Date: Fri May 25 13:52:07 2007 +0000
Add interning of unicode strings by copying the functionality from
stringobject.c.
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 <vstinner@python.org>
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
ready.
* 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.
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