'Return whether process is alive'

def is_alive(self):

    if (self is _current_process):
        return True
    assert (self._parent_pid == os.getpid()), 'can    only    test    a    child    process'
    if (self._popen is None):
        return False
    self._popen.poll()
    return (self._popen.returncode is None)
