python decimal rounding issue

Question

>>> round((611.05/10.0),2)
61.1
>>> round((611.05/10.0),3)
61.105

How can I get 61.11 ?

I tried with following but results are same

>>> ctx = decimal.getcontext()
>>> ctx.rounding = decimal.ROUND_HALF_UP

Try format(611.05 / 10.0, ".40f") - it's 61.10499999999..., slightly less than the half you're trying to round up. — jonrsharpe
– jonrsharpe, Commented Oct 12, 2021 at 22:34
You can't get 61.11, because 61.1049 should never round to 61.11. Check this stackoverflow.com/questions/588004/… — Grismar
– Grismar, Commented Oct 12, 2021 at 22:36
Welcome to the world of floating point math 0.30000000000000004.com — Samathingamajig
– Samathingamajig, Commented Oct 12, 2021 at 22:37

luigibertaco · Accepted Answer · 2021-10-12 23:21:53Z

1

The decimal context is applied to decimal calculations:

from decimal import Decimal, ROUND_HALF_UP

non_rounded = Decimal("611.05")/Decimal("10.0")
non_rounded.quantize(Decimal(".01"), rounding=ROUND_HALF_UP)

Returns

Decimal('61.11')

EDIT: using quantize instead of round reference

edited Oct 12, 2021 at 23:21

answered Oct 12, 2021 at 22:43

luigibertaco

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2 Comments

Bhavesh Odedra Over a year ago

This is working great in python3.x. But not in 2.x. It gives same.

luigibertaco Over a year ago

Decimals have their own rounding methods, I've updated the snippet with a working version on my py27 and py36

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