[Marshal Bug] Was Re: curious problem with large numbers

[Michael Spencer]

OK - I think this is it:

My last post fingering pickle was almost but not quite right*.  Actually the 
cuplrit is marshal, which produces the incorrect result that was noted.  The bug 
has nothing to do with IDLE, except that it uses marshal for inter-process 
communication.

Here's the failure case:
  >>> marshal.dumps(1e10000)
  'f\x061.#INF'
  >>> marshal.loads(_)
  1.0
  >>>

I speculate that this comes from marshal doing eval('1.#INF') rather than 
float('1.#INF'), and that it should be fixed to use float.  Alternatively, it 
could detect this special case and raise its own exception.  By analogy with 
pickle and cPickle it would make sense to raise ValueError on unmarshalling 
i.e., marshal.load(s).

  >>> import pickle
  >>> pickle.dumps(1e10000)
  'F1.#INF\n.'
  >>> pickle.loads(_)
  Traceback (most recent call last):
    File "<input>", line 1, in ?
    File "c:\python24\lib\pickle.py", line 1394, in loads
      return Unpickler(file).load()
    File "c:\python24\lib\pickle.py", line 872, in load
      dispatch[key](self)
    File "c:\python24\lib\pickle.py", line 968, in load_float
      self.append(float(self.readline()[:-1]))
  ValueError: invalid literal for float(): 1.#INF
  >>>


A more ambitious fix (which could be combined with option 1) would have the 
float constructor accept 1.#INF



Incidentally, the reason why this workaround is effective:
IDLE 1.1
  >>> 1e308*2
1.#INF
  >>>

is that it is the compiled code object (not what it evaluates to) that is marshalled

  >>> co = compile("1e308*2","<None>","single")
  >>> dis.dis(co)
    1           0 LOAD_CONST               0 (1e+308)
                3 LOAD_CONST               1 (2)
                6 BINARY_MULTIPLY
                7 PRINT_EXPR
                8 LOAD_CONST               2 (None)
               11 RETURN_VALUE
  >>> ma = marshal.dumps(co)
  >>> ma
 
'c\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00@\x00\x00\x00s\x0c\x00\x00\x00d\x00\x00d\x01\x00\x14Fd\x02\x00S(\x03\x00\x00\x00f\x061e+308i\x02\x00\x00\x00N(\x00\x00\x00\x00(\x00\x00\x00\x00(\x00\x00\x00\x00(\x00\x00\x00\x00t\x06\x00\x00\x00<None>t\x01\x00\x00\x00?\x01\x00\x00\x00s\x00\x00\x00\x00'
  >>>

Michael