:= is basically the "yes, I really mean it" version, whereas bare = might just be a simple typo.

It depends on the definition of edit distance used; they both have a unweighted Levenshtein distance of 1 from “==” (# of inserts, deletions, or substitions), but “:=” has an LCS distance of 2 vs “=” with 1.

Perhaps more importantly, “=” and “==” are more visually similar than “==” and “:=” and also easier to mistakenly type for each other.

I should have said single-character additions or deletions . == And = have a levenstein distance of 1, == and := is 2. You can't simply make a typo and change an equality check to assignment.

So, wiki defines levenstein distance as including substitution, but I was taught or at least remember it only being additions and deletions?

It is, but many intro programmers (and non-intro programmers!) often forget to use == instead of = for comparison, because in the real world, = more often implies equality, rather than assignment. So a novice might mistakenly type `if x=1:` but they would be unlikely to accidentally type `if x:=1:`.