a print bug?

[Summercoolness at gmail.com]

Summercooln... at gmail.com wrote:
> how about the discrepancy between
>
> >>> print 1.2345
>
> 1.2345
>
> >>> print "%10.3f" % 1.2345    # seems like a bug
>
>      1.234
>
> the first one, print knows enough to recognize and print it as 1.2345.
> however, in the second line, when it is round off, it doesn't know it
> is 1.2345 any more.

I think maybe this is the reason:  the first one, print will print it
out with a rounding to the 11th decimal point, therefore hiding any
floating point imperfection.

however, in the second one, print will not first round it off to the
11th decimal point with a subsequent rounding off to the 3rd decimal
point.  In that case, the floating point imperfection is manifested.
(by thinking it is 1.2344999999999999)

a question is:  since print can nicely hide and smooth out the floating
point imperfection, and probably most people prefer it that way, how
come the implementation of print "%10.3f" doesn't also do that --
eliminating the imperfection first, and then print it out accordingly.
I think one argument is the loss of precision, but we only print it,
rather than modify the number or the variable itself...   hm... say, if
a bank uses python to print out the "change that should be returned to
the customer" using print "%20.2f", then there will be a cent missing
here and there...  why not smooth out that imperfection and return that
penny to the customer?  (not that they really care).