Fix incorrect module return

Question

Fix incorrect module return

Asked 8 years ago

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2

Mathematically speaking why it happens and how to fix the following "error" in python:

>>>10.53 % 1
0.5299999999999994

I’d like to understand how the python works to obtain this value, why it occurs.

In fact to possible duplicate format the output via the command print.

But I’d like to work without the print...

Behold

Tries a = 10.53 % 1 and print("%.2f" % a) :)

– NoobSaibot

2017/10/13 at 04:33
It is a mistake to use the [error tag]. :)

– Victor Stafusa

2017/10/14 at 04:23
1

As to why this error occurred, the matter is discussed in this question: https://answall.com/q/219211/64969

– Jefferson Quesado

2017/10/14 at 17:46
1

@Jeffersonquesado 2 fantastic answers, 1 more didactic other more technical, however maybe for me to get the answer I expected, the question should have been: "How is the module calculation" that by the way : >>>> https://answall.com/questions/93092/como-%C3%A9-made-o-c%C3%A1lculo-de-matem%C3%A1tica-do-m%C3%B3dulo-em-javascript Now doing a mix I’m beginning to understand... Vlw the tip;)

– MagicHat

2017/10/15 at 03:00
@Magichat the intention was only to show why the representation give these errors. In fact, to better understand the module is much more interesting this question that you linked

– Jefferson Quesado

2017/10/15 at 03:03

2 answers

3

The 'problem' not only in python, happens in many other languages, some do not 'demonstrate' because they soon treat the result internally. This has been the subject of early computing, and has to do with a binary approximation of numbers instead of decimal.

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To be able to perform mathematical operations accurately and not just format the output you can use the module decimal

from decimal import Decimal

value = Decimal('10.53') % 1
print(value) # 0.53

DEMONSTRATION

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by Thiago Barcala • **574** points · Answer 1 · 2017-10-13T04:41:36+00:00

This is because some numbers cannot be represented exactly in floating point notation.

What you can do in this case is to approximate the number to a certain number of decimal places when showing the user:

print('%0.2f' % (10.53 % 1))

The biggest problem is whether you need to do several operations with floating points in sequence. In this case the error can increase more and more. Depending on the case, you can work with integers, multiplying the values by 100 for example, and when showing the final result, divide by 100 again and round. By doing this the error will be minimized.