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gh-129033: Remove _Py_InitializeMain() function (#129034)

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Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>
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Victor Stinner 2025-01-20 11:03:22 +01:00 • committed by GitHub
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92
Doc/c-api/init_config.rst
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@ -1946,89 +1946,13 @@ Py_GetArgcArgv()
See also :c:member:`PyConfig.orig_argv` member.
Delaying main module execution
==============================
Multi-Phase Initialization Private Provisional API
==================================================
In some embedding use cases, it may be desirable to separate interpreter initialization
from the execution of the main module.
This section is a private provisional API introducing multi-phase
initialization, the core feature of :pep:`432`:
* "Core" initialization phase, "bare minimum Python":
* Builtin types;
* Builtin exceptions;
* Builtin and frozen modules;
* The :mod:`sys` module is only partially initialized
(ex: :data:`sys.path` doesn't exist yet).
* "Main" initialization phase, Python is fully initialized:
* Install and configure :mod:`importlib`;
* Apply the :ref:`Path Configuration <init-path-config>`;
* Install signal handlers;
* Finish :mod:`sys` module initialization (ex: create :data:`sys.stdout`
and :data:`sys.path`);
* Enable optional features like :mod:`faulthandler` and :mod:`tracemalloc`;
* Import the :mod:`site` module;
* etc.
Private provisional API:
* :c:member:`PyConfig._init_main`: if set to ``0``,
:c:func:`Py_InitializeFromConfig` stops at the "Core" initialization phase.
.. c:function:: PyStatus _Py_InitializeMain(void)
Move to the "Main" initialization phase, finish the Python initialization.
No module is imported during the "Core" phase and the ``importlib`` module is
not configured: the :ref:`Path Configuration <init-path-config>` is only
applied during the "Main" phase. It may allow to customize Python in Python to
override or tune the :ref:`Path Configuration <init-path-config>`, maybe
install a custom :data:`sys.meta_path` importer or an import hook, etc.
It may become possible to calculate the :ref:`Path Configuration
<init-path-config>` in Python, after the Core phase and before the Main phase,
which is one of the :pep:`432` motivation.
The "Core" phase is not properly defined: what should be and what should
not be available at this phase is not specified yet. The API is marked
as private and provisional: the API can be modified or even be removed
anytime until a proper public API is designed.
Example running Python code between "Core" and "Main" initialization
phases::
void init_python(void)
{
PyStatus status;
PyConfig config;
PyConfig_InitPythonConfig(&config);
config._init_main = 0;
/* ... customize 'config' configuration ... */
status = Py_InitializeFromConfig(&config);
PyConfig_Clear(&config);
if (PyStatus_Exception(status)) {
Py_ExitStatusException(status);
}
/* Use sys.stderr because sys.stdout is only created
by _Py_InitializeMain() */
int res = PyRun_SimpleString(
"import sys; "
"print('Run Python code before _Py_InitializeMain', "
"file=sys.stderr)");
if (res < 0) {
exit(1);
}
/* ... put more configuration code here ... */
status = _Py_InitializeMain();
if (PyStatus_Exception(status)) {
Py_ExitStatusException(status);
}
}
This separation can be achieved by setting ``PyConfig.run_command`` to the empty
string during initialization (to prevent the interpreter from dropping into the
interactive prompt), and then subsequently executing the desired main module
code using ``__main__.__dict__`` as the global namespace.