Clean up solver choosing

There was a lot of redundant code between the specified solver cases and
the guessing solver cases. These treatements have been consolidated and
simplified. Easier to rearrange order of solvers to try and to add in new
solvers.

Addresses usnistgov#644

fipy/solvers/__init__.py

@@ -7,138 +7,108 @@
 from future.utils import text_to_native_str
 __all__ = [text_to_native_str(n) for n in __all__]
 
-solver = _parseSolver()
+_desired_solver = _parseSolver()
 
-def _envSolver(solver):
-    import os
-    if solver is None and 'FIPY_SOLVERS' in os.environ:
-        solver = os.environ['FIPY_SOLVERS'].lower()
-    return solver
-
-solver = _envSolver(solver)
+import os
+if _desired_solver is None and 'FIPY_SOLVERS' in os.environ:
+    _desired_solver = os.environ['FIPY_SOLVERS'].lower()
+
+exceptions = []
 
 class SerialSolverError(Exception):
     def __init__(self, solver):
         super(SerialSolverError, self).__init__(solver + ' does not run in parallel')
 
-if solver == "pysparse":
-    if _parallelComm.Nproc > 1:
-        raise SerialSolverError('pysparse')
-    from fipy.solvers.pysparse import *
-    __all__.extend(pysparse.__all__)
-    from fipy.matrices.pysparseMatrix import _PysparseMeshMatrix
-    _MeshMatrix =  _PysparseMeshMatrix
-
-elif solver == "petsc":
-    from fipy.solvers.petsc import *
-    __all__.extend(petsc.__all__)
-
-    from fipy.matrices.petscMatrix import _PETScMeshMatrix
-    _MeshMatrix =  _PETScMeshMatrix
-
-elif solver == "trilinos":
-    from fipy.solvers.trilinos import *
-    __all__.extend(trilinos.__all__)
-
-    try:
-        from fipy.matrices.pysparseMatrix import _PysparseMeshMatrix
-        _MeshMatrix =  _PysparseMeshMatrix
-    except ImportError:
-        from fipy.matrices.trilinosMatrix import _TrilinosMeshMatrix
-        _MeshMatrix =  _TrilinosMeshMatrix
-
-elif solver == "scipy":
-    if _parallelComm.Nproc > 1:
-        raise SerialSolverError('scipy')
-    from fipy.solvers.scipy import *
-    __all__.extend(scipy.__all__)
-    from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
-    _MeshMatrix = _ScipyMeshMatrix
-
-elif solver == "pyamg":
-    if _parallelComm.Nproc > 1:
-        raise SerialSolverError('pyamg')
-    from fipy.solvers.pyAMG import *
-    __all__.extend(pyAMG.__all__)
-    from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
-    _MeshMatrix = _ScipyMeshMatrix
-
-elif solver == "pyamgx":
-    if _parallelComm.Nproc > 1:
-        raise SerialSolverError('pyamgx')
-    from fipy.solvers.pyamgx import *
-    __all__.extend(pyamgx.__all__)
-    from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
-    _MeshMatrix = _ScipyMeshMatrix
-
-elif solver == "no-pysparse":
-    from fipy.solvers.trilinos import *
-    __all__.extend(trilinos.__all__)
-    from fipy.matrices.trilinosMatrix import _TrilinosMeshMatrix
-    _MeshMatrix =  _TrilinosMeshMatrix
-
-elif solver is None:
-    # If no argument or environment variable, try importing them and seeing
-    # what works
-
-    exceptions = []
+solver = None
 
+if solver is None and _desired_solver in ["pysparse", None]:
     try:
         if _parallelComm.Nproc > 1:
             raise SerialSolverError('pysparse')
         from fipy.solvers.pysparse import *
         __all__.extend(pysparse.__all__)
-        solver = "pysparse"
         from fipy.matrices.pysparseMatrix import _PysparseMeshMatrix
         _MeshMatrix =  _PysparseMeshMatrix
+        solver = "pysparse"
+    except Exception as inst:
+        exceptions.append(inst)
 
-    except (ImportError, SerialSolverError) as inst:
+if solver is None and _desired_solver in ["petsc", None]:
+    try:
+        from fipy.solvers.petsc import *
+        __all__.extend(petsc.__all__)
+
+        from fipy.matrices.petscMatrix import _PETScMeshMatrix
+        _MeshMatrix =  _PETScMeshMatrix
+        solver = "petsc"
+    except Exception as inst:
         exceptions.append(inst)
 
-        try:
-            from fipy.solvers.trilinos import *
-            __all__.extend(trilinos.__all__)
-            solver = "trilinos"
+if solver is None and _desired_solver in ["trilinos", "no-pysparse", None]:
+    try:
+        from fipy.solvers.trilinos import *
+        __all__.extend(trilinos.__all__)
+
+        if _desired_solver != "no-pysparse":
             try:
                 from fipy.matrices.pysparseMatrix import _PysparseMeshMatrix
                 _MeshMatrix =  _PysparseMeshMatrix
+                solver = "trilinos"
             except ImportError:
-                solver = "no-pysparse"
-                from fipy.matrices.trilinosMatrix import _TrilinosMeshMatrix
-                _MeshMatrix =  _TrilinosMeshMatrix
-        except ImportError as inst:
-            exceptions.append(inst)
+                pass
+
+        if solver is None:
+            # no-pysparse requested or pysparseMatrix failed to import
+            from fipy.matrices.trilinosMatrix import _TrilinosMeshMatrix
+            _MeshMatrix =  _TrilinosMeshMatrix
+            solver = "no-pysparse"
+    except Exception as inst:
+        exceptions.append(inst)
 
-            try:
-                if _parallelComm.Nproc > 1:
-                    raise SerialSolverError('pyamg')
-                from fipy.solvers.pyAMG import *
-                __all__.extend(pyAMG.__all__)
-                solver = "pyamg"
-                from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
-                _MeshMatrix = _ScipyMeshMatrix
-            except (ImportError, SerialSolverError) as inst:
-                exceptions.append(inst)
-
-                try:
-                    if _parallelComm.Nproc > 1:
-                        raise SerialSolverError('scipy')
-                    from fipy.solvers.scipy import *
-                    __all__.extend(scipy.__all__)
-                    solver = "scipy"
-                    from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
-                    _MeshMatrix = _ScipyMeshMatrix
-                except (ImportError, SerialSolverError) as inst:
-                    exceptions.append(inst)
-                    import warnings
-                    warnings.warn("Could not import any solver package. If you are using Trilinos, make sure you have all of the necessary Trilinos packages installed - Epetra, EpetraExt, AztecOO, Amesos, ML, and IFPACK.")
-                    for inst in exceptions:
-                        warnings.warn(inst.__class__.__name__ + ': ' + inst.message)
-
-
-else:
-    raise ImportError('Unknown solver package %s' % solver)
+if solver is None and _desired_solver in ["scipy", None]:
+    try:
+        if _parallelComm.Nproc > 1:
+            raise  SerialSolverError('scipy')
+        from fipy.solvers.scipy import *
+        __all__.extend(scipy.__all__)
+        from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
+        _MeshMatrix = _ScipyMeshMatrix
+        solver = "scipy"
+    except Exception as inst:
+        exceptions.append(inst)
+
+if solver is None and _desired_solver in ["pyamg", None]:
+    try:
+        if _parallelComm.Nproc > 1:
+            raise  SerialSolverError('pyamg')
+        from fipy.solvers.pyAMG import *
+        __all__.extend(pyAMG.__all__)
+        from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
+        _MeshMatrix = _ScipyMeshMatrix
+        solver = "pyamg"
+    except Exception as inst:
+        exceptions.append(inst)
+
+if solver is None and _desired_solver in ["pyamgx", None]:
+    try:
+        if _parallelComm.Nproc > 1:
+            raise  SerialSolverError('pyamgx')
+        from fipy.solvers.pyamgx import *
+        __all__.extend(pyamgx.__all__)
+        from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
+        _MeshMatrix = _ScipyMeshMatrix
+        solver = "pyamgx"
+    except Exception as inst:
+        exceptions.append(inst)
 
+if solver is None:
+    if _desired_solver is None:
+        raise ImportError('Unable to load a solver: %s' % [str(e) for e in exceptions])
+    else:
+        if len(exceptions) > 0:
+            raise ImportError('Unable to load solver %s: %s' % (_desired_solver, [str(e) for e in exceptions]))
+        else:
+            raise ImportError('Unknown solver package %s' % _desired_solver)
 
 from fipy.tests.doctestPlus import register_skipper