This module integrates unit systems into SymPy, allowing a user choose which system to use when doing their computations and providing utilities to display and convert units.
Unit systems are composed of units and constants, which are themselves described from dimensions and numbers, and possibly a prefix. Quantities are defined by their unit and their numerical value, with respect to the current system.
The main advantage of this implementation over the old unit module is that it divides the units in unit systems, so that the user can decide which units to use, instead of having all in the name space (for example astrophysicists can only use units with ua, Earth or Sun masses, the theoricists will use natural system, etc.). Moreover it allows a better control over the dimensions and conversions.
Ideas about future developments can be found on the Github wiki.