Cbc not found on Fedora

[TeaDrinkingProgrammer]

Summary

When using the CBC solver on Fedora, you get the following error even with the coin-or-Cbc package installed. The cause is simple: most distros name the cbc binary cbc, but Fedora names it Cbc. Pyomo always uses cbc

Steps to reproduce the issue

#!/usr/bin/env python3
"""
Minimal reproducible example for Pyomo CBC solver issue on Fedora.
"""

import shutil
import sys

print("Checking for CBC executables:")
print(f"  which cbc: {shutil.which('cbc') or 'NOT FOUND'}")
print(f"  which Cbc: {shutil.which('Cbc') or 'NOT FOUND'}")

from pyomo.environ import SolverFactory, ConcreteModel, Var, Objective

# Try to create CBC solver
solver = SolverFactory('cbc')

if not solver.available():
    print("FAILURE: Pyomo cannot find CBC solver")
    print("  Even though /usr/bin/Cbc exists!")
    sys.exit(1)

# Try to solve a simple problem
model = ConcreteModel()
model.x = Var(bounds=(0, 10))
model.obj = Objective(expr=model.x)

try:
    results = solver.solve(model)
    print(f"SUCCESS: x = {model.x.value}")
except Exception as e:
    print(f"FAILURE: {e}")
    sys.exit(1)

Gives:

Checking for CBC executables:
  which cbc: NOT FOUND
  which Cbc: /usr/bin/Cbc
FAILURE: Pyomo cannot find CBC solver
  Even though /usr/bin/Cbc exists!

Error Message

self = <pyomo.solvers.plugins.solvers.CBCplugin.CBCSHELL object at 0x7f0740772390>
exception_flag = True

    def available(self, exception_flag=False):
        """True if the solver is available"""
        if self._assert_available:
            return True
        if not OptSolver.available(self, exception_flag):
            return False
        try:
            # HACK: Suppress logged warnings about the executable not
            # being found
            cm = nullcontext() if exception_flag else LoggingIntercept()
            with cm:
                ans = self.executable()
        except NotImplementedError:
            ans = None
        if ans is None:
            if exception_flag:
                msg = "No executable found for solver '%s'"
>               raise ApplicationError(msg % self.name)
E               pyomo.common.errors.ApplicationError: No executable found for solver 'cbc'

.venv/lib/python3.12/site-packages/pyomo/opt/solver/shellcmd.py:140: ApplicationError

Information on your system

Pyomo version: 6.8.2
Python version: 3.12
Operating system: Fedora 43
How Pyomo was installed (PyPI, conda, source): UV (PyPi)
Solver (if applicable):

Additional information

[mrmundt]

Hi @TeaDrinkingProgrammer . First, I love your GitHub handle. I, too, am a tea drinking programmer.

As for this issue, thanks for reporting it! Pyomo by default searches the path for the desired executable and, as you have experienced, will yell if it can't find it. That being said, there is intentionally built-in support for passing in a custom executable if your desired program is in a different location or, in your case, has a "non-standard" name:

import pyomo.environ as pyo
solver = pyo.SolverFactory('cbc', executable='/usr/bin/Cbc')

Can you please try that and let us know if it doesn't work as intended?

[mrmundt]

@TeaDrinkingProgrammer - Were you able to try out my suggestion?