Python 2.4 (#1, Feb 22 2005, 15:02:34) 
[GCC 3.4.3-20050110 (Gentoo Linux 3.4.3.20050110,
ssp-3.4.3.20050110-0, pie-8.7 on linux2
Type "help", "copyright", "credits" or "license" for
more information.
>>> import decimal
>>> hash(decimal.NaN)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.4/decimal.py", line 720, in
__hash__
    i = int(self)
  File "/usr/lib/python2.4/decimal.py", line 1410, in
__int__
    return context._raise_error(InvalidContext)
  File "/usr/lib/python2.4/decimal.py", line 2215, in
_raise_error
    raise error, explanation
decimal.InvalidOperation

This behaviour doesn't match the comment in
decimal.py's __hash__:
# Decimal integers must hash the same as the ints
# Non-integer decimals are normalized and hashed as strings
# Normalization assures that hast(100E-1) == hash(10)

Would it make sense to wrap the int(self) in an except
block and return hash(str(self.normalize())) if this
raises?

Logged In: YES 
user_id=80475

Since two NaNs are never equal to one another, I would think
that it doesn't make sense to hash them.  Tim, do you have
another thoughts on the subject?

Logged In: YES 
user_id=31435

Well, I'm not really a fan of Python's tying hashability 
to "usable as a dict key", but given that's what Python 
_does_, ya, hashing a NaN doesn't make sense.

marienz, by "special" decimals did you mean only NaNs, or 
do you have other cases in mind too?

Logged In: YES 
user_id=1104715

NaN, Inf, and negInf all fail to hash. 

Inf and negInf are equal to themselves, so they don't have any problem 
being used as a dict key. 

As for NaN, I don't see any harm in allowing it to return a hashcode 
anyways, but perhaps you're right. 

However, in that case, it would be nice to have the exception raised be 
somewhat more regular and expected-looking than a InvalidOperation 
from int(). Perhaps it should raise TypeError('Decimal("NaN") is 
unhashable').

Logged In: YES 
user_id=80475

Fixed.  See Lib/decimal.py 1.35.

Anthony, can this be backported to 2.4.1 or does it need to
wait for 2.4.2?

Logged In: YES 
user_id=29957

If you can check it in in the next 24 hours, yes.
otherwise, it can wait til 2.4.2

Logged In: YES 
user_id=80475

Okay, it's backported.