Created on 2020-02-24 09:28 by wjzbf, last changed 2020-02-24 09:42 by steven.daprano. This issue is now closed.
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| msg362574 - (view) | Author: (wjzbf) | Date: 2020-02-24 09:28 | |
hello python, when i calculate: 151476660579404160000-151476660579404160000//1000000007 * (1e9+7) it returns 67534848.0 when i calculate 151476660579404160000 % (1e9+7) it returns 67536199.0 the two values are not equal. how to explain it? thanks zbf |
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| msg362575 - (view) | Author: Steven D'Aprano (steven.daprano) *  |
Date: 2020-02-24 09:42 | |
This is a floating point issue, not a bug. Floats inherently only have a limited precision available, so they are not always the exact number you think they are. Using 1e9 forces the result to be a float, which introduces rounding errors into the calculation. If you use an exact integer, the calculation is exact: py> 151476660579404160000-151476660579404160000//1000000007 * (10**9+7) 67543367 py> 151476660579404160000 % (10**9+7) 67543367 *This is not a Python bug* this is an inherent limitation of floating point numbers and the same issues will occur in any language that uses floats. https://docs.python.org/3/faq/design.html#why-am-i-getting-strange-results-with-simple-arithmetic-operations |
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| History | |||
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| Date | User | Action | Args |
| 2020-02-24 09:42:47 | steven.daprano | set | status: open -> closed nosy: + steven.daprano messages: + msg362575 resolution: not a bug stage: resolved |
| 2020-02-24 09:28:03 | wjzbf | create | |