About the educational problem. If someone is puzzled by "1.1*3 !=
3.3", you could always use '%50f' % 1.1 instead of repr(1.1). I don't
think that trying to teach people that floating points don't always do
what they expect them to do is a good reason to print uninteresting
and visually distracting digits when you don't have to.

About the compatibility problem: I don't see why it should matter to
the NumPy people if the repr() of some floats is made shorter. Anyway,
we can ask them, using a PEP or just the mailing list.

About the benefit: If I have data which contains floats, I'm usually
interested about their (physical) value, not about their last bits.
That's why str(f) does what it does. I like repr(x) to be one-to-one,
as I explained in the previous message, but if it can be made more
readable, why not make it so?