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A Python – SWI-Prolog bridge enabling to query SWI-Prolog


PySwip is a Python – SWI-Prolog bridge enabling to query SWI-Prolog in your Python programs. It features an (incomplete) SWI-Prolog foreign language interface, a utility class that makes it easy querying with Prolog and also a Pythonic interface.

Installing the Latest Version

The latest SWI-Prolog supported by Ubuntu 18.04 and 20.04 are 7.6.4. We generally want to support LTS releases of
Ubuntu. The compatibility of PySwip with 7.6.4 on master is broken, so we are not able to release a new version until
this is fixed. In the meantime, you can use the following to install PySwip from the master branch:

pip install git+https://github.com/yuce/[email protected]#egg=pyswip

The End of Python 2 Support

Python 2 has reached end of life on January 1st, 2020 as documented here.
So, PySwip 0.2.10 will be the last version which officially supports Python 2.

Do you still require Python 2 support? Let us know at: https://github.com/yuce/pyswip/issues/94


What’s New?

See the CHANGELOG.

WARNING! PySwip has no Windows installers! If you are a Windows user, see INSTALL. There are some “free download” sites that claim to be hosting PySwip installers. DO NOT TRUST THEM!

Thanks to all contributors.

Introduction

PySwip is a Python – SWI-Prolog bridge enabling to query SWI-Prolog in your Python programs.
It features an (incomplete) SWI-Prolog foreign language interface, a utility class that makes it easy querying with Prolog and also a
Pythonic interface.

Since PySwip uses SWI-Prolog as a shared library and ctypes to access it, it doesn’t require compilation to be installed.

Requirements:

  • Python 3.6 and higher.
  • PyPy is currently not supported.
  • SWI-Prolog 8.2 and higher.
  • libswipl as a shared library. This is the default on most platforms.
  • Works on Linux, Windows, MacOS and FreeBSD. Should work on other POSIX.

Install

IMPORTANT: Make sure the SWI-Prolog architecture is the same as the Python architecture. If you are using a 64bit build of Python, use a 64bit build of SWI-Prolog, etc.

See INSTALL for instructions.

Examples

Using Prolog

from pyswip import Prolog
prolog = Prolog()
prolog.assertz("father(michael,john)")
prolog.assertz("father(michael,gina)")
list(prolog.query("father(michael,X)")) == [{'X': 'john'}, {'X': 'gina'}]
for soln in prolog.query("father(X,Y)"):
    print(soln["X"], "is the father of", soln["Y"])
# michael is the father of john
# michael is the father of gina

An existing knowledge base stored in a Prolog file can also be consulted,
and queried. Assuming the filename “knowledge_base.pl” and the Python is
being run in the same working directory, it is consulted like so:

>>> from pyswip import Prolog
>>> prolog = Prolog()
>>> prolog.consult("knowledge_base.pl")

Foreign Functions

from __future__ import print_function
from pyswip import Prolog, registerForeign

def hello(t):
    print("Hello,", t)
hello.arity = 1

registerForeign(hello)

prolog = Prolog()
prolog.assertz("father(michael,john)")
prolog.assertz("father(michael,gina)")
print(list(prolog.query("father(michael,X), hello(X)")))

Pythonic interface (Experimental)

from __future__ import print_function
from pyswip import Functor, Variable, Query, call

assertz = Functor("assertz", 1)
father = Functor("father", 2)
call(assertz(father("michael","john")))
call(assertz(father("michael","gina")))
X = Variable()

q = Query(father("michael",X))
while q.nextSolution():
    print("Hello,", X.value)
q.closeQuery()

# Outputs:
#    Hello, john
#    Hello, gina

The core functionality of Prolog.query is based on Nathan Denny’s public domain prolog.py.

GitHub – yuce/pyswip: PySwip is a Python – SWI-Prolog bridge enabling to query SWI-Prolog in your Python programs. It features an (incomplete) SWI-Prolog foreign language interface, a utility class that makes it easy querying with Prolog and also a Pythonic interface.

PySwip is a Python – SWI-Prolog bridge enabling to query SWI-Prolog in your Python programs. It features an (incomplete) SWI-Prolog foreign language interface, a utility class that makes it easy qu…


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