dj-labeler 0.2.0

Installation

Labeler is available on Pypi as dj-labeler:

pip install dj-labeler

Example

Imagine our bookstore models look like this:

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=200)
    published = models.BooleanField(default=False)
    birthdate = models.DateField(blank=True, null=True)


class Book(models.Model):
    title = models.CharField(max_length=200)
    published_on = models.DateField(blank=True, null=True)
    isbn = models.CharField(max_length=50)
    authors = models.ManyToManyField(Author)

Now you want to branch out into a Dutch-speaking market. Instead of relying on Django’s automagical label creation based on the field name, you’ll need to explicitly state your verbose name for each field and mark it as a translatable string. And to avoid any confusion for the people performing the Dutch translation, you want to provide as much context as possible, because an author’s name might not require the same label as the name of a category.

So you end up with this:

from django.db import models
from django.utils.translation import pgettext_lazy

class Author(models.Model):
    name = models.CharField(pgettext_lazy('author', 'name'), max_length=200)
    published = models.BooleanField(pgettext_lazy('author', 'published'), editable=False)
    birthdate = models.DateField(pgettext_lazy('author', 'birthdate'), blank=True, null=True)

    class Meta:
        verbose_name = pgettext_lazy('author model', 'Author')
        verbose_name_plural = pgettext_lazy('author model (plural)', 'Authors')


class Book(models.Model):
    title = models.CharField(pgettext_lazy('book', 'title'), max_length=200)
    published_on = models.DateField(pgettext_lazy('book (date)', 'published'), blank=True, null=True)
    isbn = models.CharField(pgettext_lazy('book', 'isbn'), max_length=50)
    authors = models.ManyToManyField(Author, verbose_name=pgettext_lazy('book authors', 'authors'))

    class Meta:
        verbose_name = pgettext_lazy('author model', 'Book')
        verbose_name_plural = pgettext_lazy('author model (plural)', 'Books')

Now add in help text and you’ve got a lot of noise, making it hard to discern the attributes you as a programmer care about most when developing, like the maximum length and whether a field is optional.

Labeler will enable apps to use i18nized strings with less noise. Let’s move the strings to a separate file we’ll call i18n.py (but any name will do) and use Labeler’s ModelTranslations:

# i18n.py
from django.utils.translation import pgettext_lazy
from labeler import ModelTranslations

author = ModelTranslations(
    labels=dict(
        name=pgettext_lazy('author', 'name'),
        published=pgettext_lazy('author', 'published'),
        birthdate=pgettext_lazy('author', 'birthdate')
    )
    help_texts=dict(
        birthdate=pgettext_lazy('author', 'When was the author born?')
    ),
    name=pgettext_lazy('author model', 'Author'),
    name_plural=pgettext_lazy('author model (plural)', 'Authors')
)

book = ModelTranslations(
    labels=dict(
        title=pgettext_lazy('book', 'title'),
        published_on=pgettext_lazy('book (date)', 'published'),
        isbn=pgettext_lazy('book', 'isbn'),
        authors=pgettext_lazy('book authors', 'authors')
    ),
    help_texts=dict(
        isbn=pgettext_lazy('book', 'The ISBN will be validated against XYZ database')
    ),
    name=pgettext_lazy('author model', 'Book'),
    name_plural=pgettext_lazy('author model (plural)', 'Books')
)

That’s still a lot of noise, but at least we’ve got it isolated to a single file in our app. Now, since ModelTranslations is simply an extension of dict, you could start doing things like this:

from . import i18n

class Author(models.Model):
    # as above

    class Meta:
        verbose_name = i18n.author['name']
        verbose_name_plural = i18n.author['name_plural']

But that doesn’t cut down on the noise. Instead you should use the inject method/decorator of ModelTranslations (or FormTranslation when dealing with a form). This will make our models become lean and mean:

# models.py
from django.db import models
from labeler.models import label_with
from . import i18n

@i18n.author.inject
class Author(models.Model):
    name = models.CharField(max_length=200)
    published = models.BooleanField(default=False)
    birthdate = models.DateField(blank=True, null=True)


@i18n.book.inject
class Book(models.Model):
    title = models.CharField(max_length=200)
    published_on = models.DateField(blank=True, null=True)
    isbn = models.CharField(max_length=50)
    authors = models.ManyToManyField(Author)

The above example is equivalent to our noisy example where we first introduced internationalized strings.

Using ModelTranslations

ModelTranslations is a simple dict with some useful methods and properties added on top. Nothing is required, but if you specify labels or help_texts, the keys of those dictionaries should refer to existing model fields.

Example:

from labeler import ModelTranslations

my_model = ModelTranslations(
    labels=dict(  # verbose_name of the model's fields
        model_field_a='Something',
        model_field_b='Else'
    ),
    help_texts=dict(  # help_text of the model's fields
        model_field_a='Some help text'
    ),
    name='my model',  # verbose_name of the model
    name_plural='my models',  # verbose_name_plural of the model
    errors=dict(  # Handy dict of error messages for this model
        invalid_state='Some error'
    ),
    messages=dict(  # Handy dict for other kinds of messages
        congrats='Success!'
    ),
    something_else='abc',  # Just a dict; add whatever you want
    my_choices={
        'ok': 'Great',
        'nok': 'Eh, try again'
    }
)

When everything is good and ready to go, simply inject this on your model:

from . import i18n

@i18n.my_model.inject
class MyModel(models.Model):
    # Your fields and stuff goes here of course

The nested labels, errors, and help_texts dictionaries are also available as properties. This means custom validation might look like this:

def clean_fields(self, exclude=None):
    super(MyModel, self).clean_fields(exclude)
    if self.field not in VALID_STATE:
        raise ValidationError({'field': i18n.my_translations.errors['invalid_state']})

If you’re dealing with lots of nested dicts, you can use the resolve method:

hard_way = i18n.my_model.get('errors', {}).get('fieldname', {}).get('invalid', {}).get('state')
easier_way = i18n.my_model.resolve('errors.fieldname.invalid.state')
easier_way == hard_way

Using FormTranslations

FormTranslations works exactly like ModelTranslations, but it also supports a nested dictionary empty_labels to override the default empty label on form fields. Usage:

# i18n.py
from labeler import FormTranslations

article_form = FormTranslations(
    labels=dict(
        title='Title goes here',
        body='Text goes here',
        published='When to publish this article',
        author='Author',
    ),
    help_texts=dict(
        title='Limit to 100 characters please',
        body='Formatting is not supported'
    ),
    empty_labels=dict(
        author='Please select an author'
    )
)

# forms.py
from django import forms
from . import i18n
from .models import Article

@i18n.article_form.inject
class ArticleForm(forms.ModelForm):

    class Meta:
        model = Article
        fields = ('title', 'body', 'published', 'author')

That’s all there is to it.