Python 3 float problems?

Question

I was trying to do the follow calculation in python 3:

add with:

that should return 0 (images were made in wolframalpha).

When I try to do the same calculation in python:

pow((2*3*5),28)-29*math.floor(pow((2*3*5),28)/29)-1

it returns 4303955653455607115022335.

the value of each part is:

228767924549610000000000000000000000000000 correct.

-228767924549609995696044346544392884977665 incorrect.

How can I fix this?

Please include all the relevant code and information as **text** in the question itself, not as external images. — Thierry Lathuille, Jan 12 '20 at 19:03
Does this answer your question? [Is floating point math broken?](https://stackoverflow.com/questions/588004/is-floating-point-math-broken) — Peter Wood, Jan 12 '20 at 19:06
You can fix this by using an actual [tag:bignum] library or [the `fractions` module](https://docs.python.org/3.8/library/fractions.html) — ForceBru, Jan 12 '20 at 19:12

score 0 · Accepted Answer · answered Jan 12 '20 at 19:11

0

You are using floating point division / which has a limited precision, so your large result gets rounded.

Instead, you can get what you want with integer, floor division //, which has an integer result with unlimited precision:

import math
pow((2*3*5),28)-29*(pow((2*3*5),28)//29)-1
# 0

answered Jan 12 '20 at 19:11

Thierry Lathuille

really ty was looking for an answer and couldnt find anywhere – aesthetic Jan 12 '20 at 19:13

1 Answers1