def _select_cols(a_dict, keys):
    """Filters out entries in a dictionary that have a key which is not part of 'keys' argument. `a_dict` is not
    modified and a new dictionary is returned."""
    if keys == list(a_dict.keys()):
        return a_dict
    else:
        return {field_name: a_dict[field_name] for field_name in keys}