how to calculate float number using precision in python

Question

precision = 2
number = 31684.28
result = Decimal(number) - Decimal(10 ** -precision)
print(result)

Desired output:

31684.27

Actual output:

31684.26999999999883584657356

What I try to do is to subtract 0.01 from number.

First of all, why do you subtract precision from number? o_O — Olvin Roght, Jan 22 '21 at 07:07

David · Answer 1 · 2021-01-22T07:15:16.157

3

You should use formating like the following:

print("{:.2f}".format(result))

Or using round like:

print(round(result, 2))

comment

The question wasn't clear from the start. The correct answer (in my opinion is of @U11-Forward)

edited Jan 22 '21 at 07:15

answered Jan 22 '21 at 07:07

David

He already using `Decimal` which should solve this problem. Issue is in `10 ** -price_precision`. – Olvin Roght Jan 22 '21 at 07:08
I don't think that's what the OP wants tho... anyway he isn't clear on this – U13-Forward Jan 22 '21 at 07:11
@U11-Forward yes, he just now commented that he wanted to subtract 0.01. Wasnt clear from the start. You picked it up nicely! – David Jan 22 '21 at 07:12
@DavidS Yeah I think maybe now my answer is more *possible* to work for him – U13-Forward Jan 22 '21 at 07:12

score 3 · Answer 2 · answered Jan 22 '21 at 07:10

3

You have to make the values with Decimal(...) not the output. So try this:

from decimal import Decimal
precision = 2
number = 31684.28
result = number - float(10 ** Decimal(-precision))
print(result)

Output:

31684.27

answered Jan 22 '21 at 07:10

U13-Forward

score 1 · Answer 3 · answered Jan 22 '21 at 07:11

1

You can use the function round
The syntax is: round(number, digits)
So, result = round(number, 2)

answered Jan 22 '21 at 07:11

Virej Dasani

score 1 · Answer 4 · answered Jan 22 '21 at 07:13

1

You can use quantize method of decimal library

from decimal import Decimal


result = Decimal('31684.26999999999883584657356').quantize(Decimal('0.01'))
# result = Decimal('31684.27')

answered Jan 22 '21 at 07:13

Roman Matusevich