[Python-Dev] RFC: PEP 587 "Python Initialization Configuration": 2nd version

[Victor Stinner]

)Le lun. 13 mai 2019 à 18:28, Steve Dower <steve.dower at python.org> a écrit :
> My take:
> * all the examples are trying to be isolated from the system Python
> install (except Vim?)

"Isolation" means different things:

* ignore configuration files
* ignore environment variables
* custom path configuration (sys.path, sys.executable, etc.)

It seems like the most common need is to have a custom path configuration.

Py_IsolatedFlag isn't used. Only py2app manually ignores a few
environment variables.


> * all the examples want to import some of their own modules before
> running user code

Well, running code between Py_Initialize() and running the final
Python code is not new, and my PEP doesn't change anything here: it's
still possible, as it was previously. You can use PyRun_SimpleFile()
after Py_Initialize() for example.

Maybe I misunderstood your point.


> * nobody understands how to configure embedded Python :)

Well, that's the problem I'm trying to solve by designing an
homogeneous API, rather than scattered global configuration variables,
environment variables, function calls, etc.


> Also from my own work with/on other projects:
> * embedders need to integrate native thread management with Python threads

Sorry, I see the relationship with the initialization.


> * embedders want to use their own files/libraries

That's the path configuration, no?


> * embedders want to totally override getpath, not augment/configure it

On Python 3.7, Py_SetPath() is the closest thing to configure path
configuration. But I don't see how to override sys.executable
(Py_GetProgramFullPath), sys.prefix, sys.exec_prefix, nor (internal)
dll_path.

In the examples that I found, SetProgramName(), SetPythonHome() and
Py_SetPath() are called.

My PEP 587 allows to completely ignore getpath.c/getpath.c easily by
setting explicitly:

* use_module_search_path, module_search_paths
* executable
* prefix
* exec_prefix
* dll_path (Windows only)

If you set these fields, you fully control where Python looks for
modules. Extract of the C code:

    /* Do we need to calculate the path? */
    if (!config->use_module_search_paths
        || (config->executable == NULL)
        || (config->prefix == NULL)
#ifdef MS_WINDOWS
        || (config->dll_path == NULL)
#endif
        || (config->exec_prefix == NULL))
    {
        _PyInitError err = _PyCoreConfig_CalculatePathConfig(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

OpenOffice doesn't bother with complex code, it just appends a path to
PYTHONPATH:

    setenv("PYTHONPATH", getenv("PYTHONPATH") + ":" + path_bootstrap);

It can use PyWideStringList_Append(&config.module_search_paths,
path_bootstrap), as shown in one example of my PEP.

Victor
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