Python - pint - Can I set default type to Decimal?

Question

Im using pint module in a project. Objects in my project handle numerical data as Decimals. When I set simple pint units to a Decimal, it works:

>>> import pint
>>> from decimal import Decimal as D
>>> ureg = pint.UnitRegistry()
>>> D(10) * ureg.kN
<Quantity(10, 'kilonewton')>

But, if I try to add a second unit, it breaks. Building kiloNewton*meters in this example:

>>> D(10) * ureg.kN * ureg.m
TypeError: unsupported operand type(s) for *: 'decimal.Decimal' and 'float'

I'm using this hack:

>>> a = D(1) * ureg.kN
>>> b = D(1) * ureg.m
>>> unit_kNm = a * b
>>> D(10) * unit_kNm
<Quantity(10, 'kilonewton * meter')>

I understand why it happens. I'm looking for a solution to set up pint as I want.

echefede · Accepted Answer · 2017-07-12T11:30:25.583

3

This works:

>>> D(10) * (ureg.kN * ureg.m)
<Quantity(10, 'kilonewton * meter')>

And this too:

>>> Q = ureg.Quantity
>>> Q(D(10), "kN*m")
<Quantity(10, 'kilonewton * meter')>

edited Jul 12 '17 at 11:30

answered Jul 10 '17 at 13:09

echefede

497
4
13

score 1 · Answer 2 · answered Jul 10 '17 at 12:11

1

Type cast it to decimal

import decimal
D(10) * ureg.kN * decimal.Decimal(ureg.m)

answered Jul 10 '17 at 12:11

Vishnu Upadhyay

5,043
1
13
24

It was my first idea but: '>>> import decimal >>> D(10) * ureg.kN * decimal.Decimal(ureg.m) Traceback (most recent call last): File "", line 1, in TypeError: conversion from Unit to Decimal is not supported '' – echefede Jul 10 '17 at 12:19
try to convert it to `float` first then. – Vishnu Upadhyay Jul 10 '17 at 12:36
Doesn't work. A pint object is a unit of measure and a numerical value. You can't cast the entire object. May be another way. – echefede Jul 10 '17 at 12:55
try to find base class of `pint` object and then try to convert it. – Vishnu Upadhyay Jul 10 '17 at 12:59

score 1 · Answer 3 · answered Oct 22 '22 at 06:18

As version 0.11 of pint, you can create UnitRegistry with the non_int_type=Decimal options. All new quantities created with this UnitRegistry instance have their value represented by a Decimal instance.

Example:

import pint
from decimal import Decimal
ureg = pint.UnitRegistry(non_int_type=Decimal)
a = ureg.Quantity("5 meter")
print(type(a.magnitude))

This will show that the magnitude is of type <class 'decimal.Decimal'>.

Python - pint - Can I set default type to Decimal?

3 Answers3