Where is the definition of os.system() function?

I'm in learning mode---- this is probably a dumb question but here it is:
I know there is a system() function in os.py in python, but I can't find it in os.py in github.

According to python docs, it says that 'This is implemented by calling the Standard C function system(), and has the same limitations.'.So my question is "What is the mechanism behind this?"

code : https://github.com/python/cpython/blob/3.11/Lib/os.py

This function is written in C.

This code here (from cpython/Modules/posixmodule.c) is where os.system is defined.

#ifdef HAVE_SYSTEM
#ifdef MS_WINDOWS
/*[clinic input]
os.system -> long

    command: Py_UNICODE

Execute the command in a subshell.
[clinic start generated code]*/

static long
os_system_impl(PyObject *module, const Py_UNICODE *command)
/*[clinic end generated code: output=5b7c3599c068ca42 input=303f5ce97df606b0]*/
{
    long result;

    if (PySys_Audit("os.system", "(u)", command) < 0) {
        return -1;
    }

    Py_BEGIN_ALLOW_THREADS
    _Py_BEGIN_SUPPRESS_IPH
    result = _wsystem(command);
    _Py_END_SUPPRESS_IPH
    Py_END_ALLOW_THREADS
    return result;
}
#else /* MS_WINDOWS */
/*[clinic input]
os.system -> long

    command: FSConverter

Execute the command in a subshell.
[clinic start generated code]*/

static long
os_system_impl(PyObject *module, PyObject *command)
/*[clinic end generated code: output=290fc437dd4f33a0 input=86a58554ba6094af]*/
{
    long result;
    const char *bytes = PyBytes_AsString(command);

    if (PySys_Audit("os.system", "(O)", command) < 0) {
        return -1;
    }

    Py_BEGIN_ALLOW_THREADS
    result = system(bytes);
    Py_END_ALLOW_THREADS
    return result;
}
#endif
#endif /* HAVE_SYSTEM */

Notice the line that calls system(bytes). The system function in C is apart of the standard C library, so if you wish to learn more about the C function, you can look there.

You might be wondering, "Why is it written in C?". The answer is simple, C can easily interact with you computer, and although Python can too, another C module would be required to do this from Python. It's easier, better looking, and faster to write something like this directly in C.

In os.py there is code to look for and import such system calls:

# Any new dependencies of the os module and/or changes in path separator
# requires updating importlib as well.
if 'posix' in _names:
    name = 'posix'
    linesep = '\n'
    from posix import *
    try:
        from posix import _exit
        __all__.append('_exit')
    except ImportError:
        pass
    import posixpath as path

    try:
        from posix import _have_functions
    except ImportError:
        pass

    import posix
    __all__.extend(_get_exports_list(posix))
    del posix

This may be what you were looking for in os.py -- at least as far as answer the question why don't I see this in os.py?

posix - The most common POSIX system calls

> This module provides access to operating system functionality that is
> standardized by the C Standard and the POSIX standard (a thinly
> disguised Unix interface).