Quantity-Value 0.2.0

Quantity-Value supports calculations with physical quantities

This package provides Python support for physical quantities used in mathematical equations.

Python objects called quantity-values are used to associate a measured value with a unit of measurement. Calculations involving these objects follow the rules of quantity calculus.

The package can be used to define the quantities, and associated units of measurement, of interest in a specific problem. In that way the context in which quantity calculations are performed is well defined.

Example

Calculations involving electrical measurements can be described in terms of a simple set of base quantities, here we declare current and voltage and the dependent quantity resistance

>>> from QV import *
>>> context = Context( ("Current","I"),("Voltage","V") )
>>> Resistance = context.declare('Resistance','R','Voltage/Current')

Units can be declared in terms of these quantities

>>> ureg = UnitRegister("ureg",context)
>>>
>>> volt = ureg.unit( RatioScale(context['Voltage'],'volt','V') )
>>> amp = ureg.unit( RatioScale(context['Current'],'amp','A') )
>>> milliamp = ureg.unit( prefix.milli(amp) )
>>> ohm = ureg.unit( RatioScale(context['Resistance'],'Ohm','Ohm') )

and then quantity-values can be created and manipulated

>>> v1 = qvalue(0.10,volt)
>>> i1 = qvalue(15,milliamp)
>>> print( qresult( v1/i1 ) )
6.6666666666... Ohm

Status

The Quantity-Value package is part of a research project at the Measurement Standards Laboratory of New Zealand looking at issues in Digital Metrology.

Quantity-Value is intended as an exemplar for software that supports the concept of a physical quantity and physical quantity calculations.

The project is on-going and should not yet be considered stable. There may be substantial changes in later versions.

Documentation

The documentation for Quantity-Value can be found here.