def parse_flux_bounds(entry):
    """Return flux bounds for reaction entry.

    Detect flux bounds that are specified using the non-standardized
    kinetic law parameters which are used by many pre-FBC SBML models. The
    flux bounds are returned as a pair of lower, upper bounds. The returned
    bound is None if undefined.

    Args:
        entry: :class:`SBMLReactionEntry`.
    """
    lower_bound = None
    upper_bound = None
    for parameter in entry.kinetic_law_reaction_parameters:
        pid, name, value, units = parameter
        if pid == 'UPPER_BOUND' or name == 'UPPER_BOUND':
            upper_bound = value
        elif pid == 'LOWER_BOUND' or name == 'LOWER_BOUND':
            lower_bound = value
    return lower_bound, upper_bound
