extypes

This project provides a few enhanced types for Python:

• A "constrained set" (ordered or not)
• That's all for now.

It also provides extensions for Django (1.7 - 1.10).

It has been fully tested with all versions of Python from 2.7 to 3.4; and is distributed under the BSD license.

Links

• Package on PyPI: http://pypi.python.org/pypi/extypes
• Repository and issues on GitHub: http://github.com/rbarrois/extypes
• Doc on https://extypes.readthedocs.io/ (not available yet)

Getting started

Intall the package from PyPI, using pip:

$ pip install extypes

Or from GitHub:

$ git clone git://github.com/rbarrois/extypes
$ cd extypes
$ python setup.py install

To check that everything went fine, fire a Python shell and import extypes:

import extypes

Introduction

extypes provides a new type, ConstrainedSet.

This is a set()-like object, but values can only be taken from a specific set of options.

A ConstrainedSet is declared in a manner very similar to collections.namedtuple:

import extypes
Foods = extypes.ConstrainedSet(['eggs', 'spam', 'bacon'])

This will declare a new class, Foods, whose instances are ConstrainedSet that only accept options among 'eggs', 'spam' and 'bacon'.

Those objects can be used as simple set() objects:

>>> import extypes
>>> Foods = extypes.ConstrainedSet(['eggs', 'spam', 'bacon'])
>>> meat = Foods(['spam', 'bacon'])
>>> fresh = Foods(['bacon', 'eggs'])
>>> 'eggs' in meat
False
>>> 'eggs' in fresh
True
>>> meat & fresh
Foods(['bacon'])

As a set() object, they are mutable:

>>> import extypes
>>> Foods = extypes.ConstrainedSet(['eggs', 'spam', 'bacon'])
>>> meat = Foods(['spam', 'bacon'])
>>> meat.remove('spam')
>>> meat
Foods(['bacon'])

And iterable:

>>> import extypes
>>> Foods = extypes.ConstrainedSet(['eggs', 'spam', 'bacon'])
>>> meat = Foods(['bacon', 'spam'])
>>> list(meat)
['spam', 'bacon']

But only valid options are accepted:

>>> Foods = extypes.ConstrainedSet(['eggs', 'spam', 'bacon'])
>>> greens = Foods(['spinach']
Traceback (most recent call last):
...
ValueError: Invalid keys ['spinach'], please use a value in ['spam', 'bacon', 'eggs'].

Extensions: Django

extypes also provides custom fields for Django - compatible with Django 1.7 and upwards.

from django.db import models
import extypes
import extypes.django

Foods = extypes.ConstrainedSet(['eggs', 'spam', 'bacon'])

class Fridge(models.Model):
    contents = extypes.django.SetField(choices=Foods)

This field will simply behave as a simple ConstrainedSet.

>>> fridge = Fridge(contents=['bacon'])
>>> fridge.contents.add('eggs')
>>> fridge.save()

It is displayed in forms as a multiple choice field. In the database, it is saved as a |-separated list of enabled values (in the above example, the field is stored as |eggs|bacon|).

Note

extypes.django.SetField can also receive a choice-like list:

class Fridge(models.Model):
    contents = extypes.django.SetField(choices=[('eggs', "Eggs"), ('spam', "Spam"), ('bacon', "Yummy bacon")])

In that case, the field definition is available at Fridge.contents.set_definition:

>>> f = Fridge(contents=Fridge.contents.set_definition(['eggs', 'spam']))
>>> f.get_contents_display()
"Eggs, Spam"