:orphan:

Pint: a Python units library
============================

.. image:: _static/logo-full.jpg
   :alt: Pint: **physical quantities**
   :class: floatingflask

Pint is 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.

It has a complete test coverage. It runs in Python 2.6+ and 3.2+ 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 a text file which is simple and easy to edit.
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 symbolic, latex and pretty formatting.

**Free to choose the numerical type**: You can use any numerical type (`fraction`, `float`, `decimal`, `numpy.ndarray`, etc). NumPy is not required but supported.

**NumPy integration**: When you choose to use a NumPy ndarray, its methods and ufuncs are supported including automatic conversion of units. For example `numpy.arccos(q)` will require a dimensionless `q` and the units of the output quantity will be radian.

**Handle temperature**: conversion between units with different reference points, like positions on a map or absolute temperature scales.

**Small codebase**: easy to maintain codebase with a flat hierarchy.

**Dependency free**: it depends only on Python and its standard library.

**Python 2 and 3**: a single codebase that runs unchanged in Python 2.7+ and Python 3.0+.



User Guide
----------

.. toctree::
    :maxdepth: 1

    getting
    tutorial
    numpy
    nonmult
    wrapping
    serialization
    pitheorem
    contexts
    measurement
    defining


More information
----------------

.. toctree::
    :maxdepth: 1

    contributing
    faq


One last thing
--------------

.. epigraph::

 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 <ftp://ftp.hq.nasa.gov/pub/pao/reports/1999/MCO_report.pdf>`_



