SymPy is a symbolic algebra package written in pure Python. Its ease of install and large number of features have made it a widely used code both as a library and calculator inside the Python interpreter.
Aaron Meurer commented
Mateusz mentioned that it would be great if some of the IPython people could help us convert isympy to work with ipython 0.11.
Andy and Mateusz, I don't know if anyone other than us cares about it, but I think it would be great if we could look some more into the double dispatch ideas we talked a little about at the Enthought reception.