def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def _rmsprop_update_numpy(self, var, g, mg, rms, mom, lr, decay, momentum,
                            centered):
    rms_t = rms * decay + (1 - decay) * g * g
    if centered:
      mg_t = mg * decay + (1 - decay) * g
      denom_t = rms_t - mg_t * mg_t
    else:
      mg_t = mg
      denom_t = rms_t
    mom_t = momentum * mom + lr * g / np.sqrt(denom_t, dtype=denom_t.dtype)
    var_t = var - mom_t
    return var_t, mg_t, rms_t, mom_t