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Expert Systems for Python

Project description

pypi version tests Documentation Status

Experta is a Python library for building expert systems strongly inspired by CLIPS.

from random import choice
from experta import *

class Light(Fact):
    """Info about the traffic light."""

class RobotCrossStreet(KnowledgeEngine):
    def green_light(self):

    def red_light(self):
        print("Don't walk")

    @Rule(AS.light << Light(color=L('yellow') | L('blinking-yellow')))
    def cautious(self, light):
        print("Be cautious because light is", light["color"])
>>> engine = RobotCrossStreet()
>>> engine.reset()
>>> engine.declare(Light(color=choice(['green', 'yellow', 'blinking-yellow', 'red'])))
Be cautious because light is blinking-yellow

Migrating from Pyknow

Experta is a Pyknow fork. Just replace any pyknow references in your code/examples to experta and everything should work the same.


You can find some more examples on GitHub.




  • Resolved #10. Corner case in DepthStrategy in which the first activation of the agenda didn’t get removed.


  • Resolved #11 that was introduced with #7, that caused the same behavior under different conditions.


  • Resolved #7. In some situations last activation was removed right after entering the agenda.


  • Resolved #3. Rules should not be called with already retracted facts.


  • Drop Python 3.4 support.
  • Use setup.cfg to save all package metadata.


  • Rebranded to Experta.


  • Implemented the template system.
  • Replaced warnings by watchers messages.
  • Fixed freeze() with frozen objects.
  • Fixed unfreeze() with unfrozen objects.
  • Parametrized DefFacts via reset() kwargs.


  • Improved overall performance.


  • Added Python version 3.7 to tox.ini.
  • Monkey and bananas example.
  • Fixed bug, numeric index args gets repeated in a weird way introduced in 1.4.0.
  • Pass only the defined args in absence of kwargs.


  • Order integer facts keys after making a copy.
  • as_dict method for Fact.
  • freeze and unfreeze method documentation.
  • unfreeze method in pyknow.utils.
  • Zebra example from Clips.


  • pyknow.operator module.
  • Nested matching.
  • Added Talk ‘Sistemas Expertos en Python con PyKnow - PyConES 2017’ to docs folder.


  • Freeze fact values as the default behavior to address Issue #9.
  • Added pyknow.utils.anyof to mitigate Issue #7.
  • Raise RuntimeError if a fact value is modified after declare().
  • Added MATCH and AS objects.


  • Removing the borg optimization for P field constraints.
  • Use the hash of the check in the sorting of the nodes to always generate the same alpha part of the network.


  • Allow any kind of callable in Predicate Field Constraints (P()).


  • DNF of OR clause inside AND or Rule was implemented wrong.


  • RETE matching algorithm.
  • Better Rule decorator system.
  • Facts are dictionaries.
  • Documentation.


  • Unestable API.
  • Wrong matching algorithm.
  • Bad performance

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