[New-bugs-announce] [issue29677] 'round()' accepts a negative integer for ndigits

[ChrisRands]

New submission from ChrisRands:

With a negative integer for ndigits the output from 'round()', for example 'round(3, -2)', is always zero ('0' for 'int.__round__' and '0.0' or '-0.0' for 'float.__round__').

I think either it should raise an exception or the docs should be updated to reflect the current behavior.

The docs are currently silent on this: https://docs.python.org/3/library/functions.html#round

I don't know C, but there appears to be a note in the source about this implying it is the desired behavior but without an explanation: "For ndigits < NDIGITS_MIN, x always rounds to +-0.0.": https://github.com/python/cpython/blob/6f0eb93183519024cb360162bdd81b9faec97ba6/Objects/floatobject.c

Anyway, I can't imagine an actual use case for negative ndigits.

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messages: 288710
nosy: ChrisRands
priority: normal
severity: normal
status: open
title: 'round()' accepts a negative integer for ndigits

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29677>
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