sympy 0.7.6 was released on 2014-11-22. New ebuild including new version of the system-mpmath patch available in sage-on-gentoo overlay. The version of mpmath used in sympy is 0.18 but things are working/testing fine with 0.19.
Forgot to add, it officially supports python 3.4.
Hope to bump it during this weekend.
*sympy-0.7.6 (15 Dec 2014) 15 Dec 2014; Andrey Grozin <grozin@gentoo.org> +sympy-0.7.6.ebuild, +files/sympy-0.7.6-doc-makefile.patch: Version bump