Why not offer both and be clear about it? Rather than just "length", why not call them code points? The Python docs for "len" which can be called on a unicode string say "Return the length (the number of items) of an object.". It doesn't look like a clear and easy to use API to me.
for c in "Hello":
pass
if word[0] == 'H':
pass
This would have been an extremely controversial suggestion when python3 came out to say the least.
Codepoints is a natural way of defining unicode strings in python, and it mostly works the way you expect once you give it a bit of thought. It is lower level than, say, grapheme clusters, but its more well defined and it provides the proper primitives for dealing with all use cases.