Is an implementation of Python free to make up its own answers to
division and modulus operatons in the case of inf and nan arguments?
The standard library documentation says only that // is "rounded towards
minus infinity". The language reference says that ||:
1. |x == (x//y)*y + (x%y)|,
2. the modulus has the same sign as y, and
3. division by (either kind of) zero raises |ZeroDivisionError| .
It's consistent, but it doesn't define the operator over the full range
of potential arguments. In Python 3.8 and 3.9:
>>> from decimal import Decimal
>>> Decimal('-3.14') // Decimal('Infinity')
Decimal('-0')
>>> -3.14 // float("inf")
-1.0
>>> import math
>>> math.floor(-3.14 / float("inf"))
0
I can see sense in all three answers, as possible interpretations of
"rounded towards minus infinity", but I quite like decimal's. There seem
to be no regression tests for floor division of floats, and for modulus
only with finite arguments, perhaps intentionally.
--
Jeff Allen
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