A bug on ceil function?

asked 2025-09-08 12:07:02 +0200

Ys1123
17 ●1 ●3 ●9

A following code

from math import ceil

val = (3**38 / (2*3 - 1) - 1) / 2
print(ceil(val) - val)

return

38/5

But this is weird since the value should be $< 1$ by the definition of the ceil function.

answered 2025-09-08 16:33:47 +0200

Max Alekseyev

7258 ●10 ●61 ●177

updated 2025-09-08 18:10:55 +0200

from math import ceil imports ceil function from Python's math module. So this bug (probably related to an insufficient precision of the float number resulting from division of 3**38) has nothing to do with Sage.

If you want ceil function from Sage, use from sage.all import ceil instead.

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Comments

Thank you, you're right. Then is this a bug of Python? Should I report this?

Ys1123 ( 2025-09-08 17:02:51 +0200 )edit

It's up to you. However, I think it's not a bug but just an insufficient precision of the standard Python's float type, which you obtain as the result of division of two ints.

Max Alekseyev ( 2025-09-08 18:09:24 +0200 )edit

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