@Christian

Adding a __float__ method to datetime was entertained back in 2003, but 
was rejected.  The same reasons apply to timedelta:

"""
- A C double doesn't have enough precision for roundtrip guarantees.

- Does it really need to be automatic?  I.e., does it really need to
  be __float__()?  I'd be less against this if it was an explicit
  method, e.g. dt.asposixtime().

--Guido van Rossum (home page: http://www.python.org/~guido/)
"""

http://mail.python.org/pipermail/python-dev/2003-January/032166.html