[ZODB-Dev] Problem Storing Infinity

[Tim Peters]

[David Binger]
>>> That's interesting.
>>> It appears that pickle protocol 2 chokes on inf.

[Tim Peters]
>> As above.  BTW, why protocol 2 specifically?  Protocols 1 and 2 treat
>> floats the same way.

[David]
> I was thinking that the default protocol is 1, but I see
> now that the default is 0.

Strange, eh?  Since only protocol 0 existed at first, I suppose this
was a nod to backward compatibility.

> 2.4.2 on OS X can pickle infinity using
> protocol 0, but attempts to pickle infinity using protocols
> 1 or 2 raise a SystemError.

All of which are platform-dependent accidents.

> Pickling infinity works fine, just as you say, in 2.5,
> using any of the protocols.

Well, I meant what I said ;-):

    In 2.5, marshal and pickle (but only with protocol >= 1) can at
    least pack and unpack them reliably across most IEEE-754 boxes.

It's /still/ an accident that protocol 0 worked for you under 2.5.
WinTel is the major example of a 754 box where protocol 0 still
doesn't work under 2.5, and probably never will (Microsoft's C
implementation can't read the strings it produces for infinities or
NaNs, which pretty much dooms "text mode" pickles forever in those
cases):

Python 2.6a0 (trunk:51860, Sep 11 2006, 15:23:15) [MSC v.1310 32 bit
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import cPickle
>>> p = cPickle.dumps(1e300 * 1e300)
>>> p
'F1.#INF\n.'
>>> cPickle.loads(p)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float

>>> p = cPickle.dumps(1e300 * 1e300, 1)
>>> cPickle.loads(p)
1.#INF

So protocol 0 still fails, while protocol 1 (or higher) works, and all
of them fail on WinTel before 2.5.

> Thanks for the explanation.

Hey, it's always my pleasure to spread fear :-)