> The difference is that logging is not imported at startup. So, however
> os (and friends, there are a lot of modules in sys.modules at startup)
> is imported, it is different from how readline.so is imported.

For the record, os is imported by the _io module:

    /* put os in the module state */
    state->os_module = PyImport_ImportModule("os");
    if (state->os_module == NULL)
        goto fail;

(in Modules/_io/_iomodule.c)

This probably happens before sys.path is
adjusted/tweaked/fixed/garbled/whatever.