Physical-type correctness in scientific Python

Abstract

The representation of units and dimensions in informatics systems is barely codified and often ignored. For instance, the major languages used in scientific computing (Fortran, C and Python), have no type for dimension or unit, and so physical quantities are represented in a program by variables of type real, resulting in the possibility of unit or dimensional errors. In view of this danger, many authors have proposed language schemes for unit-checking and conversion. However, since many physical quantities have the same units, it is possible for a block of code to be unit-compatible, but still physically meaningless. We demonstrate the limitations of three Python unit-libraries and present a justification and method for checking kind-of-quantity.