> set(e2 for e1 in edits1(word) for e2 in edits1(e1))
I understand how you can say something like "f(x) for x in edits1(word)", but the way it's used above with multiple fors is making my brain hurt.
s = set()
for e1 in edits1(word):
for e2 in edits1(e1):
s.add(e2) >>> [a for a in range(3) for b in range(2)]
[0, 0, 1, 1, 2, 2]
Once you keep in mind that their order has the same meaning as with normal for loops it's not so tricky. You can even indent them that way to make that more obvious.