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How Python Compares Floats and Ints: When Equals Isn’t Really Equal (blog.codingconfessions.com)

submitted 3 months ago by abhi9u@lemmy.world to c/technology@lemmy.world

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[–] Blackmist@feddit.uk 19 points 3 months ago* (last edited 3 months ago) (3 children)

I don't think that's how most programmers expect it to work at all.

However most people would also expect 0.1+0.2==0.3 to return true, so what do I know.

Floating point is something most of us ignore until it bites us in the ass. And then we never trust it again.

[–] thebestaquaman@lemmy.world 7 points 3 months ago (2 children)

I have to admit: If you (semi-)regularly use floating point comparisons in programming, I don't know why you would ever expect 0.1 + 0.2 == 0.3 to return true. It's common practice to check abs(a - b) < tol, where tol is some small number, to the point that common unit-testing libraries have built-in methods like assertEqual(a, b, tol) specifically for checking whether floats are "equal".

[–] Pelicanen@sopuli.xyz 3 points 3 months ago

Yeah, a lot of editors throw warnings for using the equals operator with floats by default, as far as I know it's considered bad practice to do it that way.

[–] Blackmist@feddit.uk 2 points 3 months ago

The issue is a lot of people use floating point numbers, but don't even know it.

How many programmers right now are using JS, the most popular language in the world? How many of them do you think understand floating point numbers and their theoretical levels of accuracy? How many of them are unknowingly using floating points to store currency values?

How many of them could accurately predict the result of the following?

2.99+1.52==4.51
2.99+1.53==4.52
2.99+1.54==4.53

Now imagine that as code to make sure you've paid the right amount in an online store. I guarantee you there is code out there right now that won't let you finish a sale if the total of the basket adds up a certain way.

[–] muntedcrocodile@lemm.ee 3 points 3 months ago

Thats why i recon its good to keep u aware of it. Mind u i find its often fine as long as my ide and chagpt know what type it is im usually fine.

I do kinda like the rigidity of types tho. Proper Python type hints are a godsend.

[–] Miaou@jlai.lu 1 points 3 months ago

Then most people shouldn't be writing code, I don't know what else to tell you, this is probably one of the first thing you learn about FP arithmetic, and any decent compiler/linter should warn you about that.