An enum implementation for Django forms and models.
Project description
dj.choices
This is a much clearer way to specify choices for fields in models and forms. A basic example:
>>> from dj.choices import Choices
>>> class Gender(Choices):
... _ = Choices.Choice
...
... male = _("Male")
... female = _("Female")
...
>>> Gender()
[(1, u'Male'), (2, u'Female')]
>>> Gender.male
<Choice: male (id: 1)>
>>> Gender.female
<Choice: female (id: 2)>
>>> Gender.male.id
1
>>> Gender.male.desc
u'Male'
>>> Gender.male.raw
'Male'
>>> Gender.male.name
u'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")
u'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 automatically get indexes (starting with 1). The class provides several features which support the DRY principle:
An object created 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.
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, u'GPL'), (2, u'BSD'), (3, u'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, u'GPL'), (101, u'BSD'), (201, u'Apache 2'), (301, u'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, u'GPL, any'), (2, u'GPL 2'), (3, u'GPL 3'), (4, u'LGPL'),
(5, u'Affero GPL'), (101, u'BSD'), (102, u'Public domain'),
(201, u'Apache 2'), (202, u'MPL'), (301, u'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, u'GPL, any'), (2, u'GPL 2'), (3, u'GPL 3'), (4, u'LGPL'), (5, u'Affero GPL')]
Advanced functionality
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, u'German'), (2, u'English'), (3, u'French'), (4, u'Polish')]
>>> Language(filter=("en", "pl"))
[(2, u'English'), (4, u'Polish')]
This has the great advantage of keeping the IDs and sorting intact.
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)) [(u'de', 'German'), (u'en', 'English'), (u'fr', 'French'), (u'pl', 'Polish')]
Predefined choices
There are several classes of choices which are very common in web applications so they are provided already: Country, Gender and Language.
Change Log
0.8.1
old accessors temporarily restored for backward compatibility (undocumented and to be removed in 1.0)
minor documentation fixes
0.8.0
code separated from lck.django
PEP8-fied the accessor APIs
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