how about len(str)? That's one that I have used quite often. And it's a sequence-type behaviour, and is considered a basic string operation.
Maybe that is the pain of this -- we are used to standard string operations (from C, anyway), so they needed to be implemented somehow. The implementation may not have been the best way, but at least we have all the operations that most languages have.
That said, I've also known the pain of accidently iterating over a string instead of a list, and seen the pain that causes. The debugging for it can suck.