DateTime.decode() is allowing unicode strings to be assigned to 
self.value.

Python 2.4 (#2, Feb 17 2005, 09:44:14) 
[GCC 2.95.4 20020320 [FreeBSD]] on freebsd4
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>>> from xmlrpclib import *
>>> s = loads(dumps((DateTime(),), methodresponse=True))
>>> print s
((<DateTime u'20050316T16:10:20' at 81ca38c>,), None)

When this DateTime object with unicode value is subsequently 
passed to dumps(), dumps() will either return the result as a unicode 
string (which I don't believe is the correct behavior), or it will raise a 
UnicodeDecodeError.

>>> dumps(s[0])
u'<params>\n<param>\n<value><dateTime.iso8601>20050316T16:
10:20</dateTime.iso8601></value>\n</param>\n</params>\n'

(UnicodeDecodeError is raised when marshalling other unicode 
strings that do not have a simple ascii representation with the 
resultant DateTime.)

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user_id=11375

I've added the str() call to xmlrpclib in rev41594.  Thanks
for reporting this.