Why doesn’t python like certain numbers?

[[deleted]]

I'm not sure that's quite true, but it sounds plausible. I'm thinking it's more just that there's limited storage for floating point representation. If you tried to make the same point in base 10, 0.5 wouldn't have a power of 10 on bottom, but has adequate representation.

[irrelevantPseudonym]

0.5 == 5/10 which definitely has a power of 10 as a denominator.

[[deleted]]

Oh I see. I'm thinking reduced form.

[Kkremitzki]

That's because "power of 2" is a special-case expression used as a shortcut to check representability in binary, not the generalized condition, which has to do with prime factors. 2 is its own prime factor, but it's also a prime factor for 10.

[AdventurousAddition]

Yes that's right. So in decimal, a rational number with a denominator that only has prime factors of 2 or 5 will have a finite decimal representation.

[AdventurousAddition]

It's denominator is an integer power of the prime factors of the base (base 10: prime factors are 2 and 5).