PySpice is a free and open source (*) Python module which interface Python to the Ngspice and Xyce circuit simulators.
Ngspice is a fork of the famous SPICE circuit simulator, while Xyce is a SPICE compatible simulator developed by the Sandia National Laboratories.
(*) PySpice is licensed under GPLv3 therms.
PySpice implements a Ngspice binding and provides an oriented object API on top of SPICE, the simulation output is converted to Numpy arrays for convenience.
PySpice requires Python 3 and works on Linux, Windows and OS X.