PyTables is a hierarchical database package designed to efficiently manage very large amounts of data. PyTables is built on top of the HDF5 library and the numarray package. It features an object-oriented interface that, combined with natural naming and C-code generated from Pyrex sources, makes it a fast, yet extremely easy-to-use tool for interactively saving and retrieving very large amounts of data. It also provides flexible indexed access on disk to anywhere in the data.