PoSym is a Python library designed to analyze the symmetry of theoretical chemistry objects. These objects include geometrical symmetry (from atomic coordinates) functions defined in a Gassian basis (molecular orbitals, wave functions, electronic densities) and vector properties (normal modes). This library makes use of continuous symmetry ideas to provide a robust implementation that do not depend on arbitrary parameters. The result of the computation is a Python symmetry object that contains the contribution of all irreducible representations of the object expressed in the basis of the specified symmetry point group. This allows to analyze an object in the basis of any symmetry point group. Features - Use as simple calculator for irreducible representations supporting direct sum and product - Handles pseudosymmetry - Determine point symmetry from normal modes - Determine point symmetry of functions defined in gaussian basis - Compatibility with PyQchem (http://www.github.com/abelcarreras/pyqchem) Requisites - numpy - scipy - pandas - yaml