[Python-Dev] struct module and coercing floats to integers (original) (raw)

Michael Urman murman at gmail.com
Sat Jul 29 05:14:58 CEST 2006

On 7/28/06, Bob Ippolito <bob at redivi.com> wrote:

http://python.org/sf/1530559

[1] The pre-2.5 behavior should really be considered a bug, the documentation says "Return a string containing the values v1, v2, ... packed according to the given format. The arguments must match the values required by the format exactly." I wouldn't consider arbitrary floating point numbers to match the value required by an integer format exactly. Floats are not in general interchangeable with integers in Python anyway (e.g. list indexes, etc.).

While it may be a bug, it's not as hard to run into, nor as illogical as the presentation here makes it sound. The original code[1] took a float value between 0 and 2, and wanted to use pack('>H', round(value * 32768)) The workaround is a trivial change pack('>H', int(round(value * 32768))) but the timeframe is less than ideal, as working code will suddenly stop and recieve only mildly helpful error message. The fact that round returns a float rather than an int, while intentional, does not feature prominently in one's mine when the first version yielded the expected results.

I would appreciate option 2 which retains compatibility but warns that the construct is bad. I will accept any of the options, as it's clear that floats don't make sense. It's just unfortunate that the previous implementation let them through in a way the new implementation does not.

[1] http://www.sacredchao.net/quodlibet/changeset/3706

Michael

Michael Urman http://www.tortall.net/mu/blog

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