Pint is a Python package to define, operate and manipulate physical quantities:
the product of a numerical value and a unit of measurement. It allows arithmetic
operations between them and conversions from and to different units.

It is distributed with a comprehensive list of physical units, prefixes and
constants. Due to its modular design, you can extend (or even rewrite!) the
complete list without changing the source code. It supports a lot of numpy
mathematical operations without monkey patching or wrapping numpy.