'Adds a watch for the given path to monitor events specified by the
mask.
:param path:
Path to monitor
:param mask:
Event bit mask.'

def _add_watch(self, path, mask):

    wd = inotify_add_watch(self._inotify_fd, path, mask)
    if (wd == (-1)):
        Inotify._raise_error()
    self._wd_for_path[path] = wd
    self._path_for_wd[wd] = path
    return wd
