Add option to provide PROCESS solver by external package

process/solver.py

@@ -6,6 +6,7 @@
 from process.evaluators import Evaluators
 from abc import ABC, abstractmethod
 from typing import Optional, Union
+import importlib
 from pyvmcon import (
     AbstractProblem,
     Result,
@@ -233,6 +234,28 @@ def get_solver(solver_name: str = "vmcon") -> _Solver:
     if solver_name == "vmcon":
         solver = Vmcon()
     else:
-        raise ValueError(f'Unrecognised solver name argument "{solver_name}"')
+        try:
+            solver = load_external_solver(solver_name)
+        except Exception as e:
+            raise ValueError(
+                f'Solver name is not an inbuilt PROCESS solver or recognised package "{solver_name}"'
+            ) from e
 
     return solver
+
+
+def load_external_solver(package: str):
+    """Attempts to load a package of name `package`.
+
+    If a package of the name is available, return the `__process_solver__`
+    attribute of that package or raise an `AttributeError`."""
+    module = importlib.import_module(package)
+
+    solver = getattr(module, "__process_solver__", None)
+
+    if solver is None:
+        raise AttributeError(
+            f"Module {module.__name__} does not have a '__process_solver__' attribute."
+        )
+
+    return solver()