CODEWITHSUNDEEP
python-3.xfloating-pointdecimal
tom q
tom q

Reputation: 97

why does sum of decimals still have floating point errors?

Im using the decimals module to try to avoid floating point errors. From the decimal module's documentary it says:

Decimal numbers can be represented exactly. In contrast, numbers like 1.1 and 2.2 do not have exact representations in binary floating point. End users typically would not expect 1.1 + 2.2 to display as 3.3000000000000003 as it does with binary floating point.

But when I try sum with decimals, I still get those floating point errors.

decimal.Decimal(4.04)+decimal.Decimal(4.04)
>>Decimal('8.080000000000000071054273576')

Why is this?

Upvotes: 2

Views: 906

Answers (1)

Jerfov2
Jerfov2

Reputation: 5504

Try putting strings around your float literals, like so:

decimal.Decimal('4.04')+decimal.Decimal('4.04')

In the code in your question, the raw binary (base 2) "float" type is passed to Decimal. When you use strings to represent the number 4.04 for example, Decimal represents '4.04' precisely in base 10.

Upvotes: 3

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