Predicates for Python

Library for constuction predicates like (OwnedBy('alex') | OwnedBy('alice')) & HasTag('game-design') and applying them to other objects.

Motivation

I tired from reimplementation of custom predicate logic in my pet projects. So, I implemented that library.

Library focus on usability, not performance. At least, for now.

Install

pip install pydicates

Use

Minimal example

from pydicates import Predicate, common


def HasTag(tag):
    return Predicate('has_tag', tag)


def has_tag(context, tag, document):
    return tag in document['tags']


common.register('has_tag', has_tag)


document = {'tags': ('a', 'b', 'c', 'd')}


assert common(HasTag('a') & HasTag('c'), document)
assert not common(HasTag('a') & HasTag('e'), document)
assert common(HasTag('a') & ~HasTag('e'), document)
assert common(HasTag('a') & (HasTag('e') | HasTag('d')), document)

More examples can be found in ./examples directory.

See ./examples/documents_check.py for API description.

See ./tests for more examples.

Limitations

• Can not chain redefined comparisons: a < b < c is equal to (a < b) and (b < c) which translates by Python to b < c, because a < b is object (Predicate) and always True.