quantity package

quantity.forms module

class quantity.forms.UnitField(*args, **kwargs)

Bases: django.forms.models.ModelChoiceField

label_from_instance(obj)

Convert objects into strings and generate the labels for the choices presented by this object. Subclasses can override this method to customize the display of the choices.

quantity.models module

class quantity.models.Quantity(unit, value)

Bases: coolfarmtool.comparable.ComparableMixin

Combination of decimal.Decimal & Unit

as_tuple()

Generate a tuple

>>> Quantity('kg', 10).as_tuple()
(10, 'kgs')

FIXME: implement using iterator (?) instead

convert_to(to_unit, area=None)

Convert to to_unit (if possible) area parameter can be provided to convert detph to volume (to_unit=mm)

Parameters

• to_unit (Unit, str) – Unit to convert to

• area (Quantity) –

• area – Is used to convert depth to volume

Raises

TypeError if units are not compatible

Useful when you need to handle irrigation units volume = depth * area / 1000 with volume in KL, depth in mm, area in m2

readable()

As __str__ but more readble rather than consistent!

class quantity.models.QuantityField(*args, **kwargs)

Bases: django.db.models.fields.DecimalField

Two-column model field for storing a Quantity

contribute_to_class(cls, name)

Register the field with the model class it belongs to.

If private_only is True, create a separate instance of this field for every subclass of cls, even if cls is not an abstract model.

get_db_prep_save(value)

Return field’s value prepared for saving into a database.

class quantity.models.Unit(*args, **kwargs)

Bases: django.db.models.base.Model

Storage and conversion of units (e.g. “kg”)

>>> kg = Unit(name="kg")
>>> kg.save()
>>> tonne = Unit(name="tonne", conversion=kg,
>>>     conversion_factor=Decimal('0.001'))
>>> tonne.save()
>>> Quantity(tonne, 1).convert_to(kg)
<Quantity: 1000.000 kg>

Unit conversion is handled using 3 fields: see conversion, conversion_factor and conversion_intercept. The asscociated database table is cached using the Django cache, so care should be taken to invalidate the cache when updating using something other than the Django admin.

exception DoesNotExist

Bases: django.core.exceptions.ObjectDoesNotExist

exception MultipleObjectsReturned

Bases: django.core.exceptions.MultipleObjectsReturned

class quantity.models.UnitField(*args, **kwargs)

Bases: django.db.models.fields.related.ForeignKey

Store a reference to a Unit

formfield(**kwargs)

Pass limit_choices_to to the field being constructed.

Only passes it if there is a type that supports related fields. This is a similar strategy used to pass the queryset to the field being constructed.

class quantity.models.UnitGroup(id, name, description)

Bases: django.db.models.base.Model

exception DoesNotExist

Bases: django.core.exceptions.ObjectDoesNotExist

exception MultipleObjectsReturned

Bases: django.core.exceptions.MultipleObjectsReturned

class quantity.models.ValueField(*args, **kwargs)

Bases: django.db.models.fields.DecimalField

Store a decimal value with default options

formfield(**kwargs)

Specify ValueInput as widget, and define label

quantity.models.get_unit(string)

Convenience method to get unit by name

quantity.widgets module

class quantity.widgets.ValueInput(attrs=None)

Bases: quantity.widgets.RemoveTrailingZeroesMixin, django.forms.widgets.TextInput

Remove trailing zeroes when rendering field values

quantity.widgets.remove_trailing_zeroes(value)

Remove trailing zeroes from a decimal.Decimal

see http://stackoverflow.com/a/11227743/399367