dj.choicee 0.9.0

An enum implementation for Django field choices, supporting group

This is a much clearer way to specify choices for fields in models and forms. A basic example:

>>> from dj.choicee import Choices
>>> class Gender(Choices):
...   _ = Choices.Choice
...
...   male = _("Male")
...   female = _("Female")
...
>>> Gender()
[(1, 'Male'), (2, 'Female')]
>>> Gender.male
<Choice: male (id: 1)>
>>> Gender.female
<Choice: female (id: 2)>
>>> Gender.male.id
1
>>> Gender.male.desc
'Male'
>>> Gender.male.raw
'Male'
>>> Gender.male.name
'male'
>>> Gender.from_name("male")
<Choice: male (id: 1)>
>>> Gender.id_from_name("male")
1
>>> Gender.raw_from_name("male")
'Male'
>>> Gender.desc_from_name("male")
'Male'
>>> Gender.name_from_id(2)
'female'
>>> Gender.name_from_id(3)
Traceback (most recent call last):
...
ValueError: Nothing found for '3'.
>>> Gender.from_name("perez")
Traceback (most recent call last):
...
ValueError: Nothing found for 'perez'.

You define a class of choices, specifying each choice as a class attribute. Those attributes are int subclasses, numbered automatically starting with 1. The class provides several features which support the DRY principle:

• An object instantiated from the choices class is basically a list of (id, localized_description) pairs straight for consumption by Django.

• Each attribute defined can be retrieved directly from the class.

• Metadata (e.g. attribute name, raw and localized description, numeric ID) of each attribute is accessible.

• Choices which are suffixed by _ to avoid clashing with Python keywords have this suffix automatically removed in their .name attributes

• Lookup functions are available to help getting attributes or their metadata.

Note

The _ = Choices.Choice trick makes it possible for django-admin.py makemessages to find each choice description and include it in .po files for localization. It masks gettext only in the scope of the class so the rest of the module can safely use gettext or gettext_lazy. Having to specify _ each time is not a particularly pretty solution but it’s explicit. Suggestions for a better approach are welcome.

Grouping choices

One of the worst problems with choices is their weak extensibility. For instance, an application defines a group of possible choices like this:

>>> class License(Choices):
...   _ = Choices.Choice
...
...   gpl = _("GPL")
...   bsd = _("BSD")
...   proprietary = _("Proprietary")
...
>>> License()
[(1, 'GPL'), (2, 'BSD'), (3, 'Proprietary')]

All is well until the application goes live and after a while the developer wants to include LGPL. The natural choice would be to add it after gpl but when we do that, the indexing would break. On the other hand, adding the new entry at the end of the definition looks ugly and makes the resulting combo boxes in the UI sorted in a counter-intuitive way. Grouping lets us solve this problem by explicitly defining the structure within a class of choices:

>>> class License(Choices):
...   _ = Choices.Choice
...
...   COPYLEFT = Choices.Group(0)
...   gpl = _("GPL")
...
...   PUBLIC_DOMAIN = Choices.Group(100)
...   bsd = _("BSD")
...
...   OSS = Choices.Group(200)
...   apache2 = _("Apache 2")
...
...   COMMERCIAL = Choices.Group(300)
...   proprietary = _("Proprietary")
...
>>> License()
[(1, 'GPL'), (101, 'BSD'), (201, 'Apache 2'), (301, 'Proprietary')]

This enables the developer to include more licenses of each group later on:

>>> class License(Choices):
...   _ = Choices.Choice
...
...   COPYLEFT = Choices.Group(0)
...   gpl_any = _("GPL, any")
...   gpl2 = _("GPL 2")
...   gpl3 = _("GPL 3")
...   lgpl = _("LGPL")
...   agpl = _("Affero GPL")
...
...   PUBLIC_DOMAIN = Choices.Group(100)
...   bsd = _("BSD")
...   public_domain = _("Public domain")
...
...   OSS = Choices.Group(200)
...   apache2 = _("Apache 2")
...   mozilla = _("MPL")
...
...   COMMERCIAL = Choices.Group(300)
...   proprietary = _("Proprietary")
...
>>> License()
[(1, 'GPL, any'), (2, 'GPL 2'), (3, 'GPL 3'), (4, 'LGPL'),
 (5, 'Affero GPL'), (101, 'BSD'), (102, 'Public domain'),
 (201, 'Apache 2'), (202, 'MPL'), (301, 'Proprietary')]

Note the behaviour:

• the developer renamed the GPL choice but its meaning and ID remained stable

• BSD, Apache and proprietary choices have their IDs unchanged

• the resulting class is self-descriptive, readable and extensible

As a bonus, the explicitly specified groups can be used when needed:

>>> License.COPYLEFT
<ChoiceGroup: COPYLEFT (id: 0)>
>>> License.gpl2 in License.COPYLEFT.choices
True
>>> [(c.id, c.desc) for c in License.COPYLEFT.choices]
[(1, 'GPL, any'), (2, 'GPL 2'), (3, 'GPL 3'), (4, 'LGPL'),
 (5, 'Affero GPL')]

ChoiceField

Choices can be used with generic IntegerField and CharField instances. When you do that though, some minor API deficiencies show up fairly quickly. First, when you define the field, you have to instanciate the choices class and the default value has to be converted to the proper type explicitly:

color = models.IntegerField(choices=Color(), default=Color.green.id)

Second, when getting the attribute back from a model, it has to be converted to a Choice instance to do anything interesting with it:

>>> obj = Model.objects.get(pk=3)
>>> obj.color
3
>>> Color.from_id(obj.color)
<Choice: Blue (id: 3, name: blue)>

To overcome those problems a ChoiceField is available in the dj.choicee.fields package. It is based on integers on the database level but the API exposes Choice instances. This helps both on the definition side:

color = ChoiceField(choices=Color, default=Color.green)

and on the access side:

>>> obj = Model.objects.get(pk=3)
>>> obj.color
<Choice: Blue (id: 3, name: blue)>
>>> obj.color = Color.green
>>> obj.save()
>>> Model.objects.get(pk=3).color
<Choice: Green (id: 2, name: green)>

For rendering forms, the field coerces to integer values. That also means that wherever Choice instances are accepted, integers are also fine.

Advanced functionality

Filtering

The developer can specify all possible choices for future use and then filter out only the currently applicable values on choices creation:

>>> class Language(Choices):
...   _ = Choices.Choice
...
...   de = _("German")
...   en = _("English")
...   fr = _("French")
...   pl = _("Polish")
...
>>> Language()
[(1, 'German'), (2, 'English'), (3, 'French'), (4, 'Polish')]
>>> Language(filter=("en", "pl"))
[(2, 'English'), (4, 'Polish')]

This has the great advantage of keeping the IDs and sorting intact.

Custom item format

One can also change how the pairs are constructed by providing a factory function. For instance, to use the class of choices defined above for the LANGUAGES setting in settings.py, one could specify:

>>> Language(item=lambda choice: (choice.name, choice.raw))
[('de', 'German'), ('en', 'English'), ('fr', 'French'),
 ('pl', 'Polish')]

Extra attributes on choices

Each choice can receive extra arguments using the extra() method:

>>> class Python(Choices):
...   _ = Choices.Choice
...
...   cpython = _("CPython").extra(language='C')
...   pypy = _("PyPy").extra(language='Python')
...   jython = _("Jython").extra(language='Java')
...   iron_python = _("IronPython").extra(language='C#')

This adds a language attribute to each choice so you can get it back like this:

>>> Python.jython.language
'Java'

This enables polymorphic attribute access later on when using models or forms. For instance, suppose you have a simple model like:

>>> class Library(models.Model):
...   name = models.CharField(max_length=100)
...   python_kind = models.IntegerField(choices=Python(), default=Python.cpython.id)

In that case to get the implementation language back yo’d do:

>>> library = Library.objects.get(name='dj.choicee')
>>> Python.from_id(library.python_kind).language
'C'

That frees your user code of any conditionals or dictionaries that depend on the state of the choices class. If you would add another choice to it, no user code needs to be changed to support it. This also supports the DRY principle because the choices class becomes the single place where configuration of that kind is held.

Extra attributes on choice groups

Unsurprisingly, choice groups can have extra attributes as well. They are then inherited by choices in such a group and can be overriden if necessary. For instance:

>>> class ProfileChange(Choices):
...   _ = Choices.Choice
...
...   USER = Choices.Group(0).extra(icon='bookkeeping.png', is_public=True)
...   email = _("e-mail").extra(is_public=False)
...   first_name = _("first name")
...   last_name = _("last name")
...
...   BASIC_INFO = Choices.Group(10).extra(icon='bookkeeping.png', is_public=True)
...   birth_date = _("birth date").extra(icon='calendar.png')
...   gender = _("gender").extra(icon='male_female.png')
...   country = _("country")
...   city = _("city")
...
...   CONTACT_INFO = Choices.Group(20).extra(icon='contactbook.png', is_public=False)
...   skype = _("Skype ID")
...   icq = _("ICQ number")
...   msn = _("MSN login")
...   xfire = _("X-Fire login")
...   irc = _("IRC info").extra(is_public=True)

In that case proper inheritance takes place:

>>> ProfileChange.first_name.is_public
True
>>> ProfileChange.email.is_public
False
>>> ProfileChange.country.icon
'bookkeeping.png'
>>> ProfileChange.birth_date.icon
'calendar.png'

Predefined choices

There are several classes of choices which are very common in web applications so they are provided already: Country, Gender and Language.

How do I run the tests?

Install tox then run:

$ tox -e py

Change Log

1.0.0

• Pure Python 3 (drop Python 2 compatibility).

• Support only Python3.5+ and Django 2.0+

• Fork from dj.choices to new project.

Authors

• Original dj.choices author Łukasz Langa.

• Fork and drop legacy Python2 code: Nguyễn Hồng Quân.