Python Macromolecular Library (mmLib) The Python Macromolecular Library (mmLib) is a software toolkit and library of routines for the analysis and manipulation of macromolecular structural models, implemented in the Python programming language. It is accessed via a layered, object-oriented application programming interface, and provides a range of useful software components for parsing mmCIF, and PDB files, a library of atomic elements and monomers, an object-oriented data structure describing biological macromolecules, and an OpenGL molecular viewer. The mmLib data model is designed to provide easy access to the various levels of detail needed to implement high-level application programs for macromolecular crystallography, NMR, modeling, and visualization. This includes specialized classes for proteins, DNA, amino acids, and nucleic acids. Also included is a extensive monomer library, element library, and specialized classes for performing unit cell calculations combined with a full space group library.