We encountered a pretty bizarre behavior of Python 2.4.6 while decoding a 600MB long unicode string 
'data':

Python 2.4.6 (8GB RAM, 64 bit)

(Pdb) type(data)
<type 'unicode'>

(Pdb) len(data)
601794657

(Pdb) data2=data.encode('utf-8')
*** SystemError: Negative size passed to PyString_FromStringAndSize

Assuming that this has something to do with a 512MB limit:

(Pdb) data2=data[:512*1024*1024].encode('utf-8')
*** SystemError: Negative size passed to PyString_FromStringAndSize

Same bug...now with 512MB - 1 byte:

(Pdb) data2=data[:(256*1024*1024)-1].encode('utf-8')
OverflowError

Cross-check on a different Linux box (4GB RAM, 4 GB Swap, 64 bit)

ajung@blackmoon:~> python2.4
Python 2.4.5 (#1, Jun  9 2008, 10:35:12) 
[GCC 4.2.1 (SUSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> data = u'x'*601794657
>>> data2= data.encode('utf-8')
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
MemoryError

Where is this different behavior coming from?