django-pint-field 0.1.5

Pint Fields for Django and Postgres

django-pint-field

Use pint with Django's ORM

Modified from the fantastic django-pint with different goals.

Unlike django-pint, in this project we use a composite field to store both the magnitude and value of the field, along with the equivalent value in base units for lookups. For this reason, the project only works with Postgresql databases. It ensures that the units your users want to use are the units they see, while still allowing accurate comparisons of one quantity to another.

Install

pip install django_pint_field

Usage

from decimal import Decimal
from django_pint_field.units import ureg
Quantity = ureg.Quantity

# Start by creating a few Pint Quantity objects
extra_small = Quantity(1 * ureg.gram)
small = Quantity(10 * ureg.gram)
medium = Quantity(100 * ureg.gram)
large = Quantity(1000 * ureg.gram)
extra_large = Quantity(10000 * ureg.gram)

# Create a couple objects
IntegerPintFieldSaveModel.objects.create(name="small", weight=small)
IntegerPintFieldSaveModel.objects.create(name="large", weight=large)

# Perform some queries
IntegerPintFieldSaveModel.objects.filter(weight__gt=medium)
<QuerySet [<IntegerPintFieldSaveModel: large>]>

IntegerPintFieldSaveModel.objects.filter(weight__gt=extra_small)
<QuerySet [<IntegerPintFieldSaveModel: small>, <IntegerPintFieldSaveModel: large>]>

IntegerPintFieldSaveModel.objects.filter(weight__gte=small)
<QuerySet [<IntegerPintFieldSaveModel: small>, <IntegerPintFieldSaveModel: large>]>

IntegerPintFieldSaveModel.objects.filter(weight__range=(small, medium))
<QuerySet [<IntegerPintFieldSaveModel: small>]>

Valid Lookups

Other lookups will be added in the future. Currently available are:

• exact
• iexact
• gt
• gte
• lt
• lte
• range
• isnull

Aggregates

A number of aggregates have been implemented for the Django Pint Fields. Functionally they should perform for Pint Fields the same way django's default aggregates work for other field types, and each is prepended with "Pint". The aggregates include:

• PintAvg
• PintCount
• PintMax
• PintMin
• PintStdDev
• PintSum
• PintVariance

Example usage:

from django_pint_field.aggregates import PintAvg, PintCount, PintMax, PintMin, PintStdDev, PintSum, PintVariance
IntegerPintFieldSaveModel.objects.aggregate(PintAvg('weight'))
IntegerPintFieldSaveModel.objects.aggregate(PintCount('weight'))
IntegerPintFieldSaveModel.objects.aggregate(PintMax('weight'))
IntegerPintFieldSaveModel.objects.aggregate(PintMin('weight'))
IntegerPintFieldSaveModel.objects.aggregate(PintStdDev('weight'))
IntegerPintFieldSaveModel.objects.aggregate(PintSum('weight'))
IntegerPintFieldSaveModel.objects.aggregate(PintVariance('weight'))

Creating your own units

You can create your own pint units if the default units in pint are not sufficient.

Anywhere within your project (ideally in settings or a file adjacent to settings), define the custom unit registry by importing Pint's default UnitRegistry and extending it:

from pint import UnitRegistry

custom_ureg = UnitRegistry()
custom_ureg.define("custom = [custom]")
custom_ureg.define("kilocustom = 1000 * custom")

Then add the custom registry to settings:

DJANGO_PINT_FIELD_UNIT_REGISTER = custom_ureg

Model Fields

• IntegerPintField: Stores a pint measurement as an integer (-2147483648 to 2147483647).
• BigIntegerPintField: Stores a pint measurement as a big integer (-9223372036854775808 to 9223372036854775807).
• DecimalPintField: Stores a pint measurement as a decimal.

Form Fields

• IntegerPintFormField: Used in forms with IntegerPintField and BigIntegerPintField.
• DecimalPintFormField: Used in forms with DecimalPintField.

Widgets

• PintFieldWidget: Default widget for all django pint field types.

Settings

DJANGO_PINT_FIELD_DECIMAL_PRECISION

Determines whether django_pint_field should automatically set the python decimal precision for the project. If an integer greater than 0 is provided, the decimal context precision for the entire project will be set to that value. Otherwise, the precision remains at the default (usually 28).
* Type: int * Default: 0

DJANGO_PINT_FIELD_UNIT_REGISTER

The Unit Registry to use in the project. Defaults to pint.UnitRegistry.
* Type: int * Default: 0

Rounding modes (upcoming feature)

decimal.ROUND_CEILING Round towards Infinity.

decimal.ROUND_DOWN Round towards zero.

decimal.ROUND_FLOOR Round towards -Infinity.

decimal.ROUND_HALF_DOWN Round to nearest with ties going towards zero.

decimal.ROUND_HALF_EVEN Round to nearest with ties going to nearest even integer.

decimal.ROUND_HALF_UP Round to nearest with ties going away from zero.

decimal.ROUND_UP Round away from zero.

decimal.ROUND_05UP Round away from zero if last digit after rounding towards zero would have been 0 or 5; otherwise round towards zero.

Read more about rounding modes for decimals at the decimal docs

Use the test app with docker compose

Build and bring up

docker compose build
docker compose run django python manage.py migrate
docker compose run django python manage.py createsuperuser
docker compose up -d

Navigate to 127.0.0.1:8000

Test (assuming you have already performed build)

docker compose run django python manage.py test

Run psql on the Postgres database

docker compose exec postgres psql -U postgres

ToDos:

• If a unit_choices value is an alias (e.g. pounds vs pound), the form widget will show the incorrect item selected. The correct value is saved in db, though.
• Implement rounding modes