Unicode and Python - how often do you index strings?

[Chris Angelico]

A current discussion regarding Python's Unicode support centres (or
centers, depending on how close you are to the cent[er]{2} of the
universe) around one critical question: Is string indexing common?

Python strings can be indexed with integers to produce characters
(strings of length 1). They can also be iterated over from beginning
to end. Lots of operations can be built on either one of those two
primitives; the question is, how much can NOT be implemented
efficiently over iteration, and MUST use indexing? Theories are great,
but solid use-cases are better - ideally, examples from actual
production code (actual code optional).

I know the collective experience of python-list can't fail to bring up
a few solid examples here :)

Thanks in advance, all!!

ChrisA