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Created on 2021-07-21 05:18 by anthonypjshaw, last changed 2022-04-11 14:59 by admin. This issue is now closed.
| Messages (4) | |||
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| msg397922 - (view) | Author: anthony shaw (anthonypjshaw) *  |
Date: 2021-07-21 05:18 | |
Powers with negative bases do not observe the same rules that float_pow/long_pow do when it comes to returning negative results/ Example: > -2 ** 2 -4 >>> x = -2 >>> y = 2 >>> x ** y 4 >>> -2. ** 2. -4.0 >>> x = -2. >>> y = 2. >>> x ** y 4.0 Tested on 3.8, 3.9 and 3.10, they all have the same bug. |
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| msg397923 - (view) | Author: Tim Peters (tim.peters) *  |
Date: 2021-07-21 05:25 | |
The binary power operator (`**`) has higher precedence than the unary negation operator (`-`). That is, -x**y groups as -(x**y). Not a bug - that's how it was designed and how it's documented. Note that this isn't novel, either. For example, to give just one example of many, that's how Maxima does it too: (%i1) -2**3; (%o1) -8 |
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| msg397924 - (view) | Author: Steven D'Aprano (steven.daprano) * |
Date: 2021-07-21 05:26 | |
Not a bug, this is due to operator precedence. It is documented under the power operator: https://docs.python.org/3/reference/expressions.html#the-power-operator and in the operator precedence table: https://docs.python.org/3/reference/expressions.html#operator-precedence If you want to raise a negative literal to a power, you need parentheses: (-2)**2 |
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| msg397925 - (view) | Author: anthony shaw (anthonypjshaw) * |
Date: 2021-07-21 05:31 | |
Thanks! I didn't realise it applied the negative operator instead of loading the constant value. |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:59:47 | admin | set | github: 88858 |
| 2021-07-21 05:31:43 | anthonypjshaw | set | messages: + msg397925 |
| 2021-07-21 05:26:37 | steven.daprano | set | status: open -> closed nosy: + steven.daprano messages: + msg397924 resolution: not a bug stage: resolved |
| 2021-07-21 05:25:37 | tim.peters | set | nosy:
+ tim.peters messages: + msg397923 |
| 2021-07-21 05:24:49 | anthonypjshaw | set | title: Const unfolding in parser with negative numbers doesn't match float/int behaviour -> Const folding in parser with negative numbers doesn't match float/int behaviour |
| 2021-07-21 05:18:16 | anthonypjshaw | create | |