Here's is an os.scandir(path='.') implementation that iterates reading the directory on the fly instead of pre-building a list.

os.listdir's implementation should ultimately be replaced by this as:

def listdir(path=None):
    if path is None:
        return list(os.scandir())
    return list(os.scandir(path))

Though I have not yet done that in this patch so that I could compare behavior of old vs new.

Why the scandir name?  Read the libc scandir man page.  It fits.

I have tested this on POSIX (Linux).  I don't have any ability to build Windows code so I expect that still has bugs and possibly compilation issues.  Please leave comments on the 'review' link.