[Python-Dev] PEP: New timestamp formats (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Thu Feb 2 14:13:49 CET 2012

On Thu, Feb 2, 2012 at 10:45 PM, Paul Moore <p.f.moore at gmail.com> wrote:

On 2 February 2012 12:16, Victor Stinner <victor.stinner at haypocalc.com> wrote:

Let's take an NTP timestamp in format (c): (sec=0, floatpart=100000000, divisor=2**32):

Decimal(100000000) * Decimal(10)**-10 Decimal('0.0100000000') Decimal(100000000) / Decimal(2)**32 Decimal('0.023283064365386962890625') You have an error of 57%. Or do you mean that not only 2**32 should be modified, but also 100000000? How do you adapt 100000000 (floatpart) when changing the divisor (232 => 10-10)? The format (c) avoids an operation (base^exponent) and avoids loosing precision. Am I missing something? If you're using the fixed point form (fraction, exponent) then 0.023283064365386962890625 would be written as (23283064365386962890625, -23). Same precision as the (100000000, base=2, exponent=32) format.

Yeah, Victor's persuaded me that the only two integer based formats that would be sufficiently flexible are (integer, numerator, divisor) and (integer, mantissa, base, exponent). The latter allows for a few more optimised conversions in particular cases. Assuming a base of 10 would just make things unnecessarily awkward when the underlying base is 2, though.

However, I think it's even more right to not have a protocol at all and just use decimal.Decimal for arbitrary precision timestamps (explicitly requested via a flag to preserve backwards compatibility).

Cheers, Nick.

-- Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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