Pint: a Python units library¶
Pint is Python module/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 it’s modular design, you can extend (or even rewrite!) the complete list without changing the source code.
It has a complete test coverage. It runs in Python 2.7 and 3.X with no other dependency. It licensed under BSD.
Design principles¶
Although there are already a few very good Python packages to handle physical quantities, no one was really fitting my needs. Like most developers, I programed Pint to scratch my own itches.
Unit parsing: prefixed and pluralized forms of units are recognized without explicitly defining them. In other words: as the prefix kilo and the unit meter are defined, Pint understands kilometers. This results in a much shorter and maintainable unit definition list as compared to other packages.
Standalone unit definitions: units definitions are loaded from simple and easy to edit text file. Adding and changing units and their definitions does not involve changing the code.
Advanced string formatting: a quantity can be formatted into string using PEP 3101 syntax. Extended conversion flags are given to provide latex and pretty formatting.
Small codebase: small and easy to maintain codebase with a flat hierarchy. It is a single stand-alone module that can be installed as a package or added side by side to your project.
Dependency free: it depends only on Python and it’s standard library.
Python 2 and 3: a single codebase that runs unchanged in Python 2.6+ and Python 3.0+.
Experimental advanced NumPy support: While NumPy is not a requirement for Pint, when available ndarray methods and ufuncs can be used in Quantity objects.
Soon¶
Handle temperature conversion: it can convert between units with different point of reference, like positions on a map or absolute temperature scales.
Where to start¶
Note
A small technical note
The MCO MIB has determined that the root cause for the loss of the MCO spacecraft was the failure to use metric units in the coding of a ground software file, “Small Forces,” used in trajectory models. Specifically, thruster performance data in English units instead of metric units was used in the software application code titled SM_FORCES (small forces). The output from the SM_FORCES application code as required by a MSOP Project Software Interface Specification (SIS) was to be in metric units of Newtonseconds (N-s). Instead, the data was reported in English units of pound-seconds (lbf-s). The Angular Momentum Desaturation (AMD) file contained the output data from the SM_FORCES software. The SIS, which was not followed, defines both the format and units of the AMD file generated by ground-based computers. Subsequent processing of the data from AMD file by the navigation software algorithm therefore, underestimated the effect on the spacecraft trajectory by a factor of 4.45, which is the required conversion factor from force in pounds to Newtons. An erroneous trajectory was computed using this incorrect data.
Mars Climate Orbiter Mishap Investigation Phase I Report PDF