This all looks great. Nice to see any cleanup in this file.
There's some room for small performance gains while here. I've noted a few places where we can easily pull out attribute accesses to the same variables out of loops and other things.

We access a_data and b_data 3 times, so let's just pull it out into a local variable. Not a hot path, but any wins out of diff code would be good.

Let's pull these out into local variables, since we access these a lot.

Can you add Args and Returns while here?

Since we're accessing this every loop, let's pull ignore_space out.

Let's also do the same with these and everything else we're accessing from self a lot.

Small tweak: We could compare v > best first, since it avoids the math and calls, and might faster in the false case.

Let's pull a_data and b_data, out, since we use these a lot.

Hmm, / vs. // changed and we never updated this, so I know we're now going back to the original behavior, but I wonder if we'll see any subtle changes from this

"Check"