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Maybe this might help:

sage: L = [[1,2,3,4], [3,5,6,7], [7,8,9,10], [1,2,3,4]]
sage: seen = []
sage: for e in L:
....:     if e in seen:
....:         continue
....:     seen.append(e)
....:     
sage: seen
[[1, 2, 3, 4], [3, 5, 6, 7], [7, 8, 9, 10]]