Relational/Logic Programming in Python?

Question

I'm a longtime python developer and recently have been introduced to Prolog. I love the concept of using relationship rules for certain kinds of tasks, and would like to add this to my repertoire.

Are there any good libraries for logic programming in Python? I've done some searching on Google but only found the following:

jtauber's blog series on relational_python

Would love to compare to some others...thanks!

-aj

wow man... i got respect for anyone who can even read prolog! +1 — Perpetualcoder
– Perpetualcoder, Commented Dec 16, 2009 at 20:59
I gave it a try as well: github.com/evertheylen/logicpy. It tries to find a good balance between too much Python magic and too cumbersome to use. — Evert Heylen
– Evert Heylen, Commented Nov 2, 2017 at 14:55
Here is a credible "real world" example in a blog post. Looks decent, except the error messages (from validation) are done poorly (you get pass/fail, without explanation why exactly) jeffersonheard.github.io/2016/11/… — user7610
– user7610, Commented Sep 21, 2018 at 11:11

Pierre Carbonnelle · Accepted Answer · 2015-10-06 20:48:02Z

14

You may want to use pyDatalog, a logic programming library that I developed for Python implementing Datalog. It also works with SQLAlchemy to query relational databases using logic clauses.

edited Oct 6, 2015 at 20:48

answered Jul 4, 2012 at 20:11

Pierre Carbonnelle

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1 Comment

ThiefMaster Over a year ago

You need to disclose that it's your project!

Cristian Ciupitu · Accepted Answer · 2013-05-05 11:14:12Z

12

Perhaps you should google "Logic Programming in Python". Pyke looks promising:

Pyke introduces a form of Logic Programming (inspired by Prolog) to the Python community by providing a knowledge-based inference engine (expert system) written in 100% Python.

Unlike Prolog, Pyke integrates with Python allowing you to invoke Pyke from Python and intermingle Python statements and expressions within your expert system rules.

edited May 5, 2013 at 11:14

Cristian Ciupitu

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answered Dec 16, 2009 at 21:32

Richie

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2 Comments

AJ. Over a year ago

@Richie, looks like a useful package. Thanks for the pointer!

heltonbiker Over a year ago

from Pyke's page: "Pyke introduces a form of Logic Programming (inspired by Prolog) to the Python community by providing a knowledge-based inference engine (expert system) written in 100% Python."

Zhanwen Chen · Accepted Answer · 2018-11-26 05:05:48Z

8

As we are heading toward 2019, I recommend PySWIP over others recommended here. It is actively maintained and has an easy interface, unlike Pyke (9 years ago) or PyLog (6 years ago).

answered Nov 26, 2018 at 5:05

Zhanwen Chen

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1 Comment

user48956 Over a year ago

Is it straightfoward to apply tabling in PySWIP (to avoid infinite loops, etc...?), as in pyDatalog.

MRocklin · Accepted Answer · 2013-05-09 14:38:10Z

5

LogPy is an implementation of miniKanren, a relational programming language, in Python. It follows in th tradition of core.logic, the preeminent logic programming solution in Clojure. LogPy was designed for interoperability with pre-existing codebases.

answered May 9, 2013 at 14:38

MRocklin

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Comments

false · Accepted Answer · 2012-03-29 19:10:38Z

3

Another option is Yield Prolog

answered Mar 29, 2012 at 19:10

false

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greg · Accepted Answer · 2010-10-15 15:53:11Z

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You could also look at Dee, which adds relations to Python: http://www.quicksort.co.uk

answered Oct 15, 2010 at 15:53

greg

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3 Comments

andrew cooke Over a year ago

is Dee an implementation of D (as described in Date's books?)

greg Over a year ago

It is (without the object/type specifications)

Janus Troelsen Over a year ago

too bad it seems dead. looked promising

false · Accepted Answer · 2012-03-29 14:52:19Z

2

A recent Prolog implementation in Python (or rather RPython) in Pyrolog. It is still rather experimental.

answered Mar 29, 2012 at 14:52

false

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andrew cooke Over a year ago

that's very cool, but does it inter-operate with python? it is written on top of pypy, which also supports (famously) a python implementation, but it's not clear to me that implies inter-op. also, while i am here, blog.herraiz.org/archives/238 is a few years old, but listed various options (it implies pyrolog inter-op, but also sounds like it is simply assumed because of pypy, which is what i am questioning).

false Over a year ago

Proof-of-concept rather. So going with the soruces might permit that.

Bernát · Accepted Answer · 2012-11-16 10:51:07Z

2

You should also check PyLog:

http://cdsoft.fr/pylog/

It has a very clean and simple syntax and implementation.

answered Nov 16, 2012 at 10:51

Bernát

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mnoorfawi · Accepted Answer · 2020-04-15 07:43:31Z

You can have a look at pytholog. It is written in python totally with no interfaces with prolog and it mimics prolog's syntax, approach and backtracking. Simply initiate a KnowledgeBase and feed it with facts and rules then run queries.

import pytholog as pl
food_kb = pl.KnowledgeBase("food")
food_kb(["food_type(gouda, cheese)",
        "food_type(ritz, cracker)",
        "food_type(steak, meat)",
        "food_type(sausage, meat)",
        "food_type(limonade, juice)",
        "food_type(cookie, dessert)",
        "flavor(sweet, dessert)",
        "flavor(savory, meat)",
        "flavor(savory, cheese)",
        "flavor(sweet, juice)",
        "food_flavor(X, Y) :- food_type(X, Z), flavor(Y, Z)"])

print(food_kb.query(pl.Expr("food_flavor(What, sweet)")))
# [{'What': 'limonade'}, {'What': 'cookie'}]
print(food_kb.query(pl.Expr("flavor(sweet, dessert)")))
# ['Yes']

It also supports calculations and probabilities

battery_kb = pl.KnowledgeBase("battery")
battery_kb([
    "battery(dead, P) :- voltmeter(battery_terminals, abnormal, P2), P is P2 + 0.5",
    "battery(dead, P) :- electrical_problem(P), P >= 0.8",
    "battery(dead, P) :- electrical_problem(P2), age(battery, old, P3), P is P2 * P3 * 0.9",
    "electrical_problem(0.7)",
    "age(battery, old, 0.8)",
    "voltmeter(battery_terminals, abnormal, 0.3)"])

battery_kb.query(pl.Expr("battery(dead, Probability)"))
# [{'Probability': 0.8}, {'Probability': 'No'}, {'Probability': 0.504}]

It can also be used to find a path between nodes in graphs.

graph = pl.KnowledgeBase("graph")
graph([
    "edge(a, b, 6)", "edge(a, c, 1)", "edge(b, e, 4)",
    "edge(b, f, 3)", "edge(c, d, 3)", "edge(d, e, 8)",
    "edge(e, f, 2)",
    "path(X, Y, W) :- edge(X , Y, W)",
    "path(X, Y, W) :- edge(X, Z, W1), path(Z, Y, W2), W is W1 + W2"])

answer, path = graph.query(pl.Expr("path(a, f, W)"), show_path = True)
print(answer)
# [{'W': 9}, {'W': 12}, {'W': 14}]

print([x for x in path if str(x) > "Z"])
# ['d', 'b', 'e', 'c']

answer, path = graph.query(pl.Expr("path(a, e, W)"), show_path = True, cut = True)
print(answer)
# [{'W': 10}]

print([x for x in path if str(x) > "Z"])
# ['b']

Pierre Carbonnelle · Accepted Answer · 2020-05-21 09:37:57Z

0

Another option is to use in-memory relational databases. After all, SQL is the most popular relational language, and it has a lot of similarity with Prolog.

answered May 21, 2020 at 9:37

Pierre Carbonnelle

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