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Physical quantities module

Project description

Pint: makes units easy

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.

It has a complete test coverage. It runs in Python 2.7 and 3.3+ with no other dependency. It is licensed under BSD.

It is extremely easy and natural to use:

>>> import pint
>>> ureg = pint.UnitRegistry()
>>> 3 * ureg.meter + 4 *
<Quantity(3.04, 'meter')>

and you can make good use of numpy if you want:

>>> import numpy as np
>>> [3, 4] * ureg.meter + [4, 3] *
<Quantity([ 3.04  4.03], 'meter')>
>>> np.sum(_)
<Quantity(7.07, 'meter')>

Quick Installation

To install Pint, simply:

$ pip install pint

or utilizing conda with, the conda-forge channel:

$ conda install -c conda-forge pint

and then simply enjoy it!


Full documentation is available at

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 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 3.3+.
  • Advanced NumPy support: While NumPy is not a requirement for Pint, when available ndarray methods and ufuncs can be used in Quantity objects.

Pint is written and maintained by Hernan E. Grecco <>.

Other contributors, listed alphabetically, are:

(If you think that your name belongs here, please let the maintainer know)

Pint Changelog

0.9 (2019-01-12)

  • Add support for registering with matplotlib’s unit handling (Issue #317, thanks dopplershift)
  • Add converters for matplotlib’s unit support. (Issue #317, thanks Ryan May)
  • Fix unwanted side effects in auto dimensionality reduction. (Issue #516, thanks Ben Loer)
  • Allow dimensionality check for non Quantity arguments.
  • Make Quantity and UnitContainer objects hashable. (Issue #286, thanks Nevada Sanchez)
  • Fix unit tests errors with numpy >=1.13. (Issue #577, thanks cpascual)
  • Avoid error in in-place exponentiation with numpy > 1.11. (Issue #577, thanks cpascual)
  • fix compatible units in context. (thanks enrico)
  • Added warning for unsupported ufunc. (Issue #626, thanks kanhua)
  • Improve IPython pretty printers. (Issue #590, thanks tecki)
  • Drop Support for Python 2.6, 3.0, 3.1 and 3.2. (Issue #567)
  • Prepare for deprecation announced in Python 3.7 (Issue #747, thanks Simon Willison)
  • Added several new units and Systems (Issues #749, #737, )
  • Started experimental pandas support (Issue #746 and others. Thanks andrewgsavage, znicholls and others)
  • wraps and checks now supports kwargs and defaults. (Issue #660, thanks jondoesntgit)

0.8.1 (2017-06-05)

  • Add support for datetime math. (Issue #510, thanks robertd)
  • Fixed _repr_html_ in Python 2.7. (Issue #512)
  • Implemented BaseRegistry.auto_reduce_dimensions. (Issue #500, thanks robertd)
  • Fixed dimension compatibility bug introduced on Registry refactoring (Issue #523, thanks dalito)

0.8 (2017-04-16)

  • Refactored the Registry in multiple classes for better separation of concerns and clarity.
  • Implemented support for defining multiple units per define call (one definition per line). (Issue #462)
  • In pow and ipow, allow array exponents (with len > 1) when base is dimensionless. (Issue #483)
  • Wraps now gets the canonical name of the unit when passed as string. (Issue #468)
  • NumPy exp and log keeps the type (Issue #95)
  • Implemented a function decorator to ensure that a context is active (with_context) (Issue #465)
  • Add warning when a System contains an unknown Group. (Issue #472)
  • Add conda-forge installation snippet. (Issue #485, thanks stadelmanma)
  • Properly support floor division and modulo. (Issue #474, thanks tecki)
  • Measurement Correlated variable fix. (Issue #463, thanks tadhgmister)
  • Implement degree sign handling. (Issue #449, thanks iamthad)
  • Change UndefinedUnitError to inherit from AttributeError (Issue #480, thanks jhidding)
  • Simplified travis for faster testing.
  • Fixed order units in siunitx formatting. (Issue #441)
  • Changed Systems lister to return a list instead of frozenset. (Issue #425, thanks GloriaVictis)
  • Fixed issue with negative values in to_compact() method. (Issue #443, thanks nowox)
  • Improved defintions. (Issues #448, thanks gdonval)
  • Improved Parser to support capital “E” on scientific notation. (Issue #390, thanks javenoneal)
  • Make sure that prefixed units are defined on the registry when unpickling. (Issue #405)
  • Automatic unit names translation through babel. (Issue #338, thanks alexbodn)
  • Support pickling Unit objects. (Issue #349)
  • Add support for wavenumber/kayser in spectroscopy context. (Issue #321, thanks gerritholl)
  • Improved formatting. (thanks endolith and others)
  • Add support for inline comments in definitions file. (Issue #366)
  • Implement Unit.__deepcopy__. (Issue #357, thanks noahl)
  • Allow changing shape for Quantities with numpy arrays. (Issue #344, thanks tecki)

0.7.2 (2016-03-02)

  • Fixed backward incompatibility problem when parsing dimensionless units.

0.7.1 (2016-02-23)

  • Use NIST as source for most of the unit information.
  • Added message to assertQuantityEqual.
  • Added detection of circular dependencies in definitions.

0.7 (2016-02-20)

  • Added Systems and groups. (Issue #215, #315)
  • Implemented references for wraps decorator. (Issue #195)
  • Added check decorator to UnitRegistry. (Issue #283, thanks kaidokert)
  • Added compact conversion. (See #224, thanks Ryan Dwyer)
  • Added compact formating code. (Issue #240)
  • New Unit Class. (thanks Matthieu Dartiailh)
  • Refactor UnitRegistry. (thanks Matthieu Dartiailh)
  • Move definitions, errors, and converters into their own modules. (thanks Matthieu Dartiailh)
  • UnitsContainer is now immutable (Issue #202, thanks Matthieu Dartiailh)
  • New parser and evaluator. (Issue #226, thanks Aaron Coleman)
  • Added support for Unicode identifiers.
  • Added m_as as way top retrieve the magnitude in different units. (Issue #227)
  • Added Short form for magnitude and units. (Issue #234)
  • Improved deepcopy. (Issue #252, thanks Emilien Kofman)
  • Improved testing infrastructure.
  • Improved docs. (thanks Ryan Dwyer, Martin Thoma, Andrea Zonca)
  • Fixed short names on electron_volt and hartree.
  • Fixed definitions of scruple and drachm. (Issue #262, thanks takowl)
  • Fixed troy ounce to 480 ‘grains’. (thanks elifab)
  • Added ‘quad’ as a unit of energy (= 10**15 Btu). (thanks Ed Schofield)
  • Added “hectare” as a supported unit of area and ‘ha’ as the symbol for hectare. (thanks Ed Schofield)
  • Added peak sun hour and Langley. (thanks Ed Schofield)
  • Added photometric units: lumen & lux. (Issue #230, thanks janpipek)
  • A fraction magnitude quantity is conserved (Issue #323, thanks emilienkofman)
  • Improved conversion performance by removing unnecessart try/except. (Issue #251)
  • Added to_tuple and from_tuple to facilitate serialization.
  • Fixed support for NumPy 1.10 due to a change in the Default casting rule (Issue #320)
  • Infrastructure: Added doctesting.
  • Infrastructure: Better way to specify exclude matrix in travis.

0.6 (2014-11-07)

  • Fix operations with measurments and user defined units. (Issue #204)
  • Faster conversions through caching and other performance improvements. (Issue #193, thanks MatthieuDartiailh)
  • Better error messages on Quantity.__setitem__. (Issue #191)
  • Fixed abbreviation of fluid_ounce. (Issue #187, thanks hsoft)
  • Defined Angstrom symbol. (Issue #181, thanks JonasOlson)
  • Removed fetching version from git repo as it triggers XCode installation on OSX. (Issue #178, thanks deanishe)
  • Improved context documentation. (Issue #176 and 179, thanks rsking84)
  • Added Chemistry context. (Issue #179, thanks rsking84)
  • Fix help(UnitRegisty) (Issue #168)
  • Optimized “get_dimensionality” and “get_base_name”. (Issue #166 and #167, thanks jbmohler)
  • Renamed ureg.parse_units parameter “to_delta” to “as_delta” to make clear. that no conversion happens. Accordingly, the parameter/property “default_to_delta” of UnitRegistry was renamed to “default_as_delta”. (Issue #158, thanks dalit)
  • Fixed problem when adding two uncertainties. (thanks dalito)
  • Full support for Offset units (e.g. temperature) (Issue #88, #143, #147 and #161, thanks dalito)

0.5.2 (2014-07-31)

  • Changed travis config to use miniconda for faster testing.
  • Added wheel configuration to setup.cfg.
  • Ensure resource streams are closed after reading.
  • Require setuptools. (Issue #169)
  • Implemented real, imag and T Quantity properties. (Issue #171)
  • Implemented __int__ and __long__ for Quantity (Issue #170)
  • Fixed SI prefix error on ureg.convert. (Issue #156, thanks jdreaver)
  • Fixed parsing of multiparemeter contexts. (Issue #174)

0.5.1 (2014-06-03)

  • Implemented a standard way to change the registry used in unpickling operations. (Issue #148)
  • Fix bug where conversion would fail due to caching. (Issue #140, thanks jdreaver)
  • Allow assigning Not a Number to a quantity array. (Issue #127)
  • Decoupled Quantity in place and not in place unit conversion methods.
  • Return None in functions that modify quantities in place.
  • Improved testing infrastructure to check for unwanted warnings.
  • Added test function at the package level to run all tests.

0.5 (2014-05-07)

  • Improved test suite helper functions.
  • Print honors default format w/o format(). (Issue #132, thanks mankoff)
  • Fixed sum() by treating number zero as a special case. (Issue #122, thanks rec)
  • Improved behaviour in ScaleConverter, OffsetConverter and (Issue #120)
  • Reimplemented loading of default definitions to allow Pint in a cx_freeze or similar package. (Issue #118, thanks jbmohler)
  • Implemented parsing of pretty printed units. (Issue #117, thanks jpgrayson)
  • Fixed representation of dimensionless quantities. (Issue #112, thanks rec)
  • Raise error when invalid formatting code is given. (Issue #111, thanks rec)
  • Default registry to lazy load, raise error on redefinition (Issue #108, thanks rec, aepsil0n)
  • Added condensed format. (Issue #107, thanks rec)
  • Added UnitRegistry () operator to parse expression replacing []. (Issue #106, thanks rec)
  • Optional case insensitive unit parsing. (Issue #105, thanks rec, jeremyfreeman, dbrnz)
  • Change the Quantity mutability depending on magnitude type. (Issue #104, thanks rec)
  • Implemented API to list compatible units. (Issue #89)
  • Implemented cache of key UnitRegistry methods.
  • Rewrote the Measurement class to use uncertainties. (Issue #24)

0.4.2 (2014-02-14)

  • Python 2.6 support (Issue #96, thanks tiagocoutinho)
  • Fixed symbol for inch. (Issue #102, thanks cybertoast)
  • Stop raising AttributeError when wrapping funcs without all of the attributes. (Issue #100, thanks jturner314)
  • Fixed warning appearing in Py2.x when comparing a Numpy Array with an empty string. (Issue #98, thanks jturner314)
  • Add links to AUR packages in docs. (Issue #91, thanks jturner314)
  • Fixed garbage collection related problem. (Issue #92, thanks jturner314)

0.4.1 (2014-01-12)

  • Integer Division with Arrays. (Issue #80, thanks jdreaver)
  • Improved Documentation. (Issue #83, thanks choloepus)
  • Removed ‘h’ alias for hour due to conflict with Planck’s constant. (Issue #82, thanks choloepus)
  • Improved get_base_units for non-multiplicative units. (Issue #85, thanks exxus)
  • Refactored code for multiplication. (Issue #84, thanks jturner314)
  • Removed ‘R’ alias for roentgen as it collides with molar_gas_constant. (Issue #87, thanks rsking84)
  • Improved naming of temperature units and multiplication of non-multiplicative units. (Issue #86, tahsnk exxus)

0.4 (2013-12-17)

  • Introduced Contexts: relation between incompatible dimensions. (Issue #65)
  • Fixed get_base_units for non multiplicative units. (Related to issue #66)
  • Implemented default formatting for quantities.
  • Changed comparison between Quantities containing NumPy arrays. (Issue #75) - BACKWARDS INCOMPATIBLE CHANGE
  • Fixes for NumPy 1.8 due to changes in handling binary ops. (Issue #73)

0.3.3 (2013-11-29)

  • ParseHelper can now parse units named like python keywords. (Issue #69)
  • Fix comparison of quantities. (Issue #74)
  • Fix Inequality operator. (Issue #70, thanks muggenhor)
  • Improved travis configuration. (thanks muggenhor)

0.3.2 (2013-10-22)

  • Fix get_dimensionality for non multiplicative units. (Issue #66)
  • Proper handling of @import directive inside a file read using pkg_resources. (Issue #68)

0.3.1 (2013-09-15)

  • fix right division on python 2.7 (Issue #58, thanks natezb)
  • fix formatting of fractional exponentials between 0 and 1. (Issue #62, thanks jdreaver)
  • fix installation as egg. (Issue #61)
  • fix handling of strange values as input of Quantity. (Issue #53)
  • math operations between quantities of different registries now raise a ValueError. (Issue #52)

0.3 (2013-09-02)

  • support for IPython autocomplete and rich display. (Issues #30 and #31)
  • support for @import directive in definitions file. (Issue #22)
  • support for wrapping functions to make them pint-aware. (Issue #16)
  • support for comparing UnitsContainer to string. (Issue #35)
  • fix error raised while converting from a single unit to one expressed as the relation between many. (Issue #29)
  • fix error raised when unit symbol is missing. (Issue #41)
  • fix error raised when magnitude is Decimal. (Issue #46, thanks danielsokolowski)
  • support for non-installed pint. (Issue #42, thanks danielsokolowski)
  • support for application of numpy function on non-ndarray magnitudes. (Issue #44)
  • support for math operations on dimensionless Quantities (written with units). (Issue #45)
  • fix obtaining dimensionless quantity from string. (Issue #50)
  • fix adding and comparing numbers to a dimensionless quantity (written with units). (Issue #54)
  • Support for iter in Quantity. (Issue #55, thanks natezb)

0.2.1 (2013-07-02)

  • fix error raised while converting from a single unit to one expressed as the relation between many. (Issue #29)

0.2 (2013-05-13)

  • support for Measurement (Quantity +/- error).
  • implemented buckingham pi theorem for dimensional analysis.
  • support for temperature units and temperature difference units.
  • parser can infers if the user mean temperature or temperature difference.
  • support for derived dimensions (e.g. [speed] = [length] / [time]).
  • refactored the code into multiple files.
  • refactored code to isolate definitions and converters.
  • refactored formatter out of UnitParser class.
  • added tox and travis config files for CI.
  • comprehensive NumPy testing including almost all ufuncs.
  • full NumPy support (features is not longer experimental).
  • fixed bug preventing from having independent registries. (Issue #10, thanks bwanders)
  • forces real division as default for Quantities. (Issue #7, thanks dbrnz)
  • improved default unit definition file. (Issue #13, thanks r-barnes)
  • smarter parser supporting spaces as multiplications and other nice features. (Issue #13, thanks r-barnes)
  • moved testsuite inside package.
  • short forms of binary prefixes, more units and fix to less than comparison. (Issue #20, thanks muggenhor)
  • pint is now zip-safe (Issue #23, thanks muggenhor)

Version 0.1.3 (2013-01-07)

  • abbreviated quantity string formating.
  • complete Python 2.7 compatibility.
  • implemented pickle support for Quantities objects.
  • extended NumPy support.
  • various bugfixes.

Version 0.1.2 (2012-08-12)

  • experimenal NumPy support.
  • included default unit definitions file. (Issue #1, thanks fish2000)
  • better testing.
  • various bugfixes.
  • fixed some units definitions. (Issue #4, thanks craigholm)

Version 0.1.1 (2012-07-31)

  • better packaging and installation.

Version 0.1 (2012-07-26)

  • first public release.

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