floating point rounding

[greg]

John Henry wrote:

> Or more precisely:
> 
> round(0.014999999999999999,2)

No, that *won't* solve the problem. Using a slightly
different example,

 >>> x = 1.5 * 0.1
 >>> x
0.15000000000000002
 >>> round(x, 2)
0.14999999999999999

The problem is that floats are stored internally in
binary, not decimal, and numbers like 0.1 and 0.01
have no exact representation as a binary float.
Using round() doesn't help, because the result is
still a binary float, and the result you're after
still can't be represented.

The best you can do is to *display* it rounded
to the number of digits you want using formatting,
e.g.

 >>> "%.2f" % x
'0.15'

Alternatively, use the Decimal module, which stores
numbers as decimal and does arithmetic in ways that
will match your calculator. It's slower, though.

--
Greg