[issue39871] math.copysign raises SystemError with non-float x and custom y

[David Vo]

New submission from David Vo <david.vo2 at gmail.com>:

If math.copysign(x, y) is passed an x that cannot be converted to a float and a y that implements __float__() in Python, math.copysign() will raise a SystemError from the TypeError resulting from the attempted float conversion of x.

math.copysign() should probably return immediately if converting the first argument to a float raises an error.

Example:

>>> import math
>>> from fractions import Fraction
>>> float(Fraction(-1, 1))  # this is needed to avoid an AttributeError?
-1.0
>>> math.copysign((-1) ** 0.5, Fraction(-1, 1))
TypeError: can't convert complex to float

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/numbers.py", line 291, in __float__
    return self.numerator / self.denominator
SystemError: PyEval_EvalFrameEx returned a result with an error set

----------
components: Extension Modules
messages: 363477
nosy: auscompgeek
priority: normal
severity: normal
status: open
title: math.copysign raises SystemError with non-float x and custom y
type: behavior

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39871>
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