metaset 1.1.2

Links

• Package on PyPI: http://pypi.python.org/pypi/metaset/

• Source on GitHub: http://github.com/Polyconseil/metaset/

• Build on Travis CI: http://travis-ci.org/lionel-panhaleux/metaset/

Quickstart

Install the package from PyPI, using pip:

pip install metaset

Or from GitHub:

git clone git://github.com/Polyconseil/metaset.git

Import it in your code:

>>> from metaset import MetaSet

Usage is quite straight forward, basic set operations are supported via the binary operators + - | ^.

>>> from pprint import pprint
>>> pprint(MetaSet(a={1, 2}, b={3}) | MetaSet(b={4}, c={5}))
{'a': {1, 2}, 'b': {3, 4}, 'c': {5}}

Django Postgres

A custom Django field is available. Note it is only available with PostgreSQL≥9.4 and Psycopg2≥2.5.4, as it is stored as a JSONB column. It is quite straightforward:

>>> from metaset.django_field import MetaSetField
>>> from django.db import models        # doctest: +SKIP

>>> class MyModel(models.Model):        # doctest: +SKIP
        mset = MetaSetField()           # doctest: +SKIP

It is compatible with the following versions:

• Django 1.7, Python 2.7, 3.4 (requires jsonfield)

• Django 1.8, Python 2.7, 3.5 (requires jsonfield)

• Django 1.9, Python 2.7, 3.5

• Django 1.10, Python 2.7, 3.5

Note when you use Django>=1.9 you have access to JSON-specific lookups not available when using jsonfield on earlier versions:

>>> MyModel.objects.filter(mset__a__contains=[1, 2])            # doctest: +SKIP
>>> MyModel.objects.filter(mset__a__contained_by=range(10))     # doctest: +SKIP
>>> MyModel.objects.filter(mset__has_key='a')                   # doctest: +SKIP
>>> MyModel.objects.filter(mset__has_keys=('a', 'b'))           # doctest: +SKIP
>>> MyModel.objects.filter(mset__has_any_keys=('a', 'b'))       # doctest: +SKIP

Detailed considerations

They are two ways to consider the “dict of sets” notion, differing on how you handle the empty values for keys.

The easiest idea is to consider that a key with no content is non-existent. This is how the dictset package is implemented.

In this alternative implementation, we chose to keep the empty keys as meaningful elements, allowing for smart unions and intersections.

>>> pprint(MetaSet(a={1}) | MetaSet(a={2}, b=set()))
{'a': {1, 2}, 'b': set()}

>>> MetaSet(a={1}) & MetaSet(a={2}, b={3})
{'a': set()}

So, beware of how empty-keys are handled, and consider using dictset if it is a better match for your use case. The behavior for subtraction and symmetric difference, although sound on a mathematical point of view, may not be what you want.

>>> MetaSet(a={1}) - MetaSet(a={1})
{'a': set()}

>>> MetaSet(a={1}) ^ MetaSet(a={1})
{'a': set()}