try: from functools import reduce except: pass data = { 'des_system_lib': set('std synopsys std_cell_lib des_system_lib dw02 dw01 ramlib ieee'.split()), 'dw01': set('ieee dw01 dware gtech'.split()), 'dw02': set('ieee dw02 dware'.split()), 'dw03': set('std synopsys dware dw03 dw02 dw01 ieee gtech'.split()), 'dw04': set('dw04 ieee dw01 dware gtech'.split()), 'dw05': set('dw05 ieee dware'.split()), 'dw06': set('dw06 ieee dware'.split()), 'dw07': set('ieee dware'.split()), 'dware': set('ieee dware'.split()), 'gtech': set('ieee gtech'.split()), 'ramlib': set('std ieee'.split()), 'std_cell_lib': set('ieee std_cell_lib'.split()), 'synopsys': set(), } def toposort2(data): for k, v in data.items(): v.discard(k) # Ignore self dependencies extra_items_in_deps = reduce(set.union, data.values()) - set(data.keys()) data.update({item:set() for item in extra_items_in_deps}) while True: ordered = set(item for item,dep in data.items() if not dep) if not ordered: break yield ' '.join(sorted(ordered)) data = {item: (dep - ordered) for item,dep in data.items() if item not in ordered} assert not data, "A cyclic dependency exists amongst %r" % data print ('\n'.join( toposort2(data) ))