python
Consider adding public PyLong_FlipSign() function
Feature or enhancement
Proposal:
Currently there is only a slow way (i.e. PyNumber_Negative()) to invert the sign of a big integer. Direct manipulation of the sign value is available only via private function, e.g. _PyLong_SetSignAndDigitCount():
https://github.com/aleaxit/gmpy/blob/1c0d4f38d4f1093df0e9460d82e4331d3d3946b6/src/gmpy2_convert_gmp.c#L153
I propose this interface:
int PyLong_FlipSign(PyObject *obj);
For small integers it will fallback to PyLong_FromLong() (like _PyLong_Negate() does), for the rest - just _PyLong_FlipSign() to change sign in place.
Alternatively, we could just expose a direct wrapper of _PyLong_FlipSign() and warn users to not use this function for small ints (that doesn't make sense for me anyway).
In both variants, on success - flip the sign of obj and return 0. On failure - return -1 with exception set. Shouldn't fail on PyLongObject or it's subtype.
I'll work on a patch if this proposal does make sense.
Has this already been discussed elsewhere?
This is a minor feature, which does not need previous discussion elsewhere
Links to previous discussion of this feature:
No response
Linked PRs
- gh-120489
I planned to propose adding PyLong_NegativeInPlace() and PyLong_AbsoluteInPlace().
Hmm, it seems that my first variant can't be implemented with same signature as the second. Rather it should be (like _PyLong_Negate()):
int PyLong_FlipSign(PyObject **obj);
adding PyLong_NegativeInPlace() and PyLong_AbsoluteInPlace().
I think this naming better fits case, when there will be also other PyNumber_*-like functions. But I'm not sure that we have practical need for that.
FYI, PR: https://github.com/python/cpython/pull/120489 (as a draft; IIUC, this should be discussed in C-API WG)
PR closed in favor of https://github.com/python/cpython/pull/121339.
Now I don't have a strong motivation for this function. Kept open as @serhiy-storchaka planned a similar proposal.
Python int objects are immutable. I dislike APIs which seem to treat them as mutable objects.
What's the status of this issue? PEP 757 has been implementation in Python 3.14. Can we close this issue?
