procutil: rewrite popen() as a subprocess.Popen wrapper (issue4746) (API) os.popen() of Python 3 is not the popen() we want. First, it doesn't accept command in bytes. Second, a returned stream is always wrapped by TextIO. So we have to reimplement our popen(). Fortunately, this fixes the bug 4746 since ours returns an exit code compatible with explainexit(). .. api:: ``procutil.popen()`` no longer supports text mode I/O.