python 2.7 string format to decimal as round function

Question

I got a problem in string format function which I don't understand. Please help to explain why and how to fix this. thanks. ( python 2.7.3 , [GCC 4.6.3] on linux2 , ubuntu 12.04 x86 )

>>> import locale
>>> locale.format("%0.{0}f".format(2), 1.135, grouping=True)
'1.14'
>>> locale.format("%0.{0}f".format(2), 1.125, grouping=True)
'1.12'

>>> ("%0.2f")%(1.135)
'1.14'
>>> ("%0.2f")%(1.125)
'1.12'

I need the format result to match the round() function

>>> round(1.135, 2)
1.14
>>> round(1.125, 2)
1.13

Thank everyone.

Answer 1

That's because rounding is not simply bringing the last digit greater than 5 up, while truncating those lower than 4, since this method would introduce an increase in the expected average of rounded numbers.

The solution is to use Bankers' Rounding, that's what you see here.