workaround for an error-looking rouding

Question

$ python
Python 2.7.3 (default, Apr 19 2012, 11:28:02) 
[GCC 4.5.3 20120403 (ALT Linux 4.5.3-alt3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> g = 1.175
>>> "%0.2f" % g
'1.18'
>>> g = 11.175
>>> "%0.2f" % g
'11.18'

So far, so good. But now:

>>> g = 111.175
>>> "%0.2f" % g
'111.17'

"111.17" instead of the expected "111.18". I think I understand what and why happens, but I need ideas how to get the expected result. Both Excel and OpenOffice Calc show "111.18", therefore somehow it should be possible.

Answer 1

You can use the decimal module here:

>>> import decimal
>>> myothercontext = decimal.Context(rounding=decimal.ROUND_HALF_UP)
>>> decimal.setcontext(myothercontext)
>>> TWOPLACES = decimal.Decimal(10) ** -2
>>> decimal.Decimal('111.175').quantize(TWOPLACES)
Decimal('111.18')
>>> decimal.Decimal('1.175').quantize(TWOPLACES)
Decimal('1.18')
>>> decimal.Decimal('11.175').quantize(TWOPLACES)
Decimal('11.18')