def edge_type_to_class(edge_type):
    """Return the edge class for layout purposes based on the edge type"""
    if 'Amount' in edge_type:
        return 'amount'
    if edge_type in ('Activation', 'Inhibition'):
        return 'activity'
    if edge_type == 'Complex':
        return 'complex'
    else:
        return 'modification'
