[Python-Dev] Re: marshal / unmarshal

[Scott David Daniels]

Terry Reedy wrote:
> "Tim Peters" <tim.peters at gmail.com> wrote in message 
> news:1f7befae0504081638145d3b4c at mail.gmail.com...
> 
>>All Python behavior in the presence of a NaN, infinity, or signed zero
>>is a platform-dependent accident.
> 
> 
> The particular issue here is not platform dependence as such but 
> within-platform usage dependence, as in the same code giving radically 
> different answers in a standard interactive console window and an idle 
> window, or when you run it the first time (from xx.py) versus subsequent 
> times (from xx.pyc) until you edit the file again. (I verified this on 2.2, 
> but MSpencer claimed to have tested on 2.4).  Having the value of an 
> expression such as '100 < 1e1000' flip back and forth between True and 
> False from run to run *is* distressing for some people ;-).
> 
> I know that this has come up before as 'wont fix' bug, but it might be 
> better to have invalid floats like 1e1000, etc, not compile and raise an 
> exception (at least on Windows) instead of breaking the reasonable 
> expectation that unmarshal(marshal(codeob)) == codeob.  That would force 
> people (at least on Windows) to do something more more within-platform 
> deterministic.
> 
> 
>>If marshal could reliably detect a NaN, then of course unmarshal
>>should reliably reproduce the NaN -- provided the platform on which
>>it's unpacked supports NaNs
> 
> 
> Windows seems to support +- INF just fine, doing arithmetic and comparisons 
> 'correctly'.  So it seems that detection or reproduction is the problem.
> 
> Terry J. Reedy
> 
> 
> 
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I can write the Windows-dependent detect code if that is what is wanted.
I just want to know what the consensus is on the "should."  If we cause
exceptions, should they be one encode or decode or both?  If not, do we
replicate all NaNs, Infs of both signs, Indeterminates?....

--Scott David Daniels
Scott.Daniels at Acm.Org