From a previous discussion, it's OK to have separate source for this, because upstream doesn't support building Python 2 and 3 packages from the same release tarball:Please can someone upload the new package python3-sympyIt's already in the team svn:
Package name : python3-sympy
Version : 0.7.2-2
URL : http://sympy.org/
Binary packages: python3-sympy
svn://svn.debian.org/python-modules/packages/python3-sympy/trunk/
http://lists.debian.org/debian-python/2012/10/msg00041.html