Eric Snow <ericsnowcurren...@gmail.com> added the comment:

## Background ##

`_Py_Identifier` (and `_Py_IDENTIFIER()`, etc.) was added in 2011 [1][2] for 
several reasons:

* provide a consistent approach for a common optimization: caching C-string 
based string objects
* facilitate freeing those objects during runtime finalization

The solution involved using a static variable defined, using `_Py_IDENTIFIER()` 
near the code that needed the string.  The variable (a `_Py_Identifier`) would 
hold the desired C string (statically initialized) and the corresponding 
(lazily created) `PyUnicodeObject`.  The code where the `_Py_Identifier` was 
defined would then pass it to specialized versions of various C-API that would 
normally consume a C string or `PyUnicodeObject`.  Then that code would use 
either the C-string or the object (creating and caching it first if not done 
already).  This approach decentralized the caching but also provided a single 
tracking mechanism that made it easier to clean up the objects.

Over the last decade a number of changes were made, including recent changes to 
make the identifiers per-interpreter and to use a centralized cache.


[1] 
https://github.com/python/cpython/commit/afe55bba33a20f87a58f940186359237064b428f
[2] 
https://mail.python.org/archives/list/python-...@python.org/message/FRUTTE47JO2XN3LXV2J4VB5A5VILILLA/

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<https://bugs.python.org/issue46541>
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