def _construct_chain_iterators(n_sample, chain_iterator_class, n_chain=None):
    """Set up chain iterator progress bar object(s)."""
    if n_chain is None:
        return chain_iterator_class(n_iter=n_sample, description='Chain 1/1')
    else:
        return [
            chain_iterator_class(
                n_iter=n_sample, description=f'Chain {c+1}/{n_chain}',
                position=(c, n_chain)) for c in range(n_chain)]