clingo

5.8.0 verified Mon Apr 27 auth: no python

CFFI-based Python bindings to the clingo Answer Set Programming (ASP) solver. Version 5.8.0, released 2024-04-06. Cadence: irregular, roughly annual.

pip install clingo

Common errors

error ModuleNotFoundError: No module named 'clingo' ↓

cause Clingo installed from PyPI may not work on systems without a compatible C compiler or prebuilt wheel (e.g., ARM macOS).

fix

Install via conda: conda install -c potassco clingo, or install from source with proper dependencies.

error clingo.core.SolveError: undefined arithmetic operation ↓

cause Using arithmetic expressions on ungrounded variables (e.g., `X = Y + 1`) without proper grounding.

fix

Use #const directives, or ground the program properly, or avoid arithmetic on variables without domain bounds.

Warnings

breaking From clingo 5.5 to 5.6, the `solve` method changed from returning a `SolveResult` to a `SolveHandle` with a context manager. In 5.4 and earlier, `ctl.solve()` returned a `SolveResult` directly. ↓

fix Use the context manager: `with ctl.solve(yield_=True) as handle:` instead of `result = ctl.solve()`.

breaking The `clingo.solving.SolveResult` class was removed in 5.6. `solve()` now returns a `SolveHandle`, and the satisfiability is obtained via `solve()`'s return value after the context manager exits. ↓

fix After the `with` block, use `handle.get()` to get satisfiability (e.g., `print(handle.get().satisfiable)`).

deprecated The `clingo.Control.load()` method is deprecated in 5.8 in favor of `Control.add()` + `Control.ground()`. ↓

fix Replace `ctl.load('file.lp')` with `with open('file.lp') as f: ctl.add('base', [], f.read()); ctl.ground([('base', [])])`.

gotcha Calling `Control.solve()` without `yield_=True` will not return models; you must iterate over the `SolveHandle` or use the context manager with `yield_=True`. ↓

fix Always use `with ctl.solve(yield_=True) as handle: for model in handle: print(model)`.

Imports

Control

wrong

import clingo; ctl = clingo.Control()

correct

from clingo import Control

Direct class import is conventional.

Function

wrong

from clingo.symbol import Function

correct

from clingo import Function

Function is in clingo, not a submodule.

Quickstart

Basic ASP solving: add rules, ground, and iterate over stable models.

from clingo import Control
ctl = Control()
ctl.add("base", [], "a :- not b. b :- not a.")
ctl.ground([("base", [])])
with ctl.solve(yield_=True) as handle:
    for model in handle:
        print(model)