There are currently four interfaces to Python. Two use direct linking and two use network communication. These are

• pyswip
  Pyswip is the oldest interface than embeds SWI-Prolog into Python based on Python's ctype package.
• Janus
  Janus is both a Python and SWI-Prolog plugin that allows for embedding Python into SWI-Prolog as well as the other way around. Janus is bundled with SWI-Prolog for embedding Python into SWI-Prolog. The Python module is available on PyPi.
• MQI
  Machine Query Interface is a library that makes SWI-Prolog accessible using JSON. It comes with a client for Python.
• Pengines
  (Prolog Engines) is bundled with SWI-Prolog, providing remote access to SWI-Prolog over HTTP. It is the basic building block for SWISH. The SWISH repository provides pointers to client libraries in various languages, including Python.

Janus is by far the most powerful of the alternatives. It is developed with the XSB and Ciao teams, creating a de-facto standard Python interface for several Prolog systems. Janus provides fast bi-directional calling between Prolog and Python. The SWI-Prolog version supports SWI-Prolog dicts, strings, unbounded integers, rational numbers and Prolog threads. The main disadvantage of Janus is that it relies on the SWI-Prolog and Python C embedding API. This implies that binaries of the interface are bound to a specific version of Python and SWI-Prolog.