Question

I understand due to the inexact representation of floating points, the following code ‘feels’ inconsistent.

"%.1f" % 1.14 # => 1.1
"%.1f" % 1.15 # => 1.1
"%.1f" % 1.16 # => 1.2
"%.0f" % 1.4 # => 1
"%.0f" % 1.5 # => 2
"%.0f" % 1.6 # => 2

However, is there an easy way of doing consistent floating points rounding by 5? One way might be to do string manipulation explicitly. Is there an easier way or existent library?

Answer 1

If you want decimal precision, use BigDecimal instead of floats.

Edit: You will have to manually round the number to the desired length before passing it to %, otherwise it gets converted to a normal float before being rounded.

"%.1f" % BigDecimal('1.15').round(1) => "1.2"
"%.0f" % BigDecimal('1.5').round(0) => "2"