[issue1580] Use shorter float repr when possible

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

For what it's worth, I'm -0.1 (or should that be -0.10000000000000001?) on 
this change.  It seems better to leave the problems caused by binary 
floating-point out in the open than try to partially hide them, and the 
proposed change just seems a little bit too 'magic'.  The inconsistency in 
the following current behaviour *does* irk me slightly (but only 
slightly):

>>> 0.13
0.13
>>> 0.14
0.14000000000000001

But practical issues aside, my preference would be to go to the other 
extreme: fix this inconsistency by changing the first output to 
0.13000000000000000 rather than changing the second output to 0.14.  That 
is, have repr(float) *always* output 17 digits, possibly except when that 
float is *exactly* representable in 16 or fewer decimal digits (e.g. 3.5, 
0.125, ...).  All the zeros act as a subtle reminder that the stored value 
is not exactly 0.13.  But I suspect this, too, isn't very practical.

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