Enable import fipy without any solver packages.

Collect exceptions thrown by ``ImportError``s in
source:fipy/solver/__init__.py and throw a warning and the exceptions
as warnings in the case when no solvers are available.

 * Moved a number of solver imports inside the calling methods in term
   classes.

fipy/models/levelSet/surfactant/adsorbingSurfactantEquation.py

@@ -39,7 +39,6 @@
 from fipy.variables.cellVariable import CellVariable
 from fipy.models.levelSet.surfactant.surfactantEquation import SurfactantEquation
 from fipy.terms.implicitSourceTerm import ImplicitSourceTerm
-from fipy.solvers import DefaultAsymmetricSolver, LinearPCGSolver
 
 __all__ = ["AdsorbingSurfactantEquation"]
 
@@ -368,6 +367,7 @@ def solve(self, var, boundaryConditions=(), solver=None, dt=None):
                 from fipy.solvers.pyAMG.linearGeneralSolver import LinearGeneralSolver
                 solver = LinearGeneralSolver(tolerance=1e-15, iterations=2000)
             else:
+                from fipy.solvers import LinearPCGSolver
                 solver = LinearPCGSolver()
 
         SurfactantEquation.solve(self, var, boundaryConditions=boundaryConditions, solver=solver, dt=dt)
@@ -390,6 +390,7 @@ def sweep(self, var, solver=None, boundaryConditions=(), dt=None, underRelaxatio
         for coeff in self.coeffs:
             coeff._updateDt(dt)
         if solver is None:
+            from fipy.solvers import DefaultAsymmetricSolver
             solver = DefaultAsymmetricSolver()
         return SurfactantEquation.sweep(self, var, solver=solver, boundaryConditions=boundaryConditions, dt=dt, underRelaxation=underRelaxation, residualFn=residualFn)
 

fipy/models/levelSet/surfactant/surfactantEquation.py

@@ -37,7 +37,6 @@
 
 from fipy.terms.transientTerm import TransientTerm
 from fipy.terms.explicitUpwindConvectionTerm import ExplicitUpwindConvectionTerm
-from fipy.solvers import DefaultAsymmetricSolver
 
 from fipy.models.levelSet.surfactant.convectionCoeff import _ConvectionCoeff
 
@@ -83,6 +82,7 @@ def solve(self, var, boundaryConditions = (), solver=None, dt=None):
         if type(boundaryConditions) not in (type(()), type([])):
             boundaryConditions = (boundaryConditions,)
         if solver is None:
+            from fipy.solvers import DefaultAsymmetricSolver
             solver=DefaultAsymmetricSolver()
 
         var.constrain(0, var.mesh.exteriorFaces)
@@ -111,6 +111,7 @@ def sweep(self, var, solver=None, boundaryConditions=(), dt=None, underRelaxatio
         if type(boundaryConditions) not in (type(()), type([])):
             boundaryConditions = (boundaryConditions,)
         if solver is None:
+            from fipy.solvers import DefaultAsymmetricSolver
             solver=DefaultAsymmetricSolver()
 
         var.constrain(0, var.mesh.exteriorFaces)

fipy/solvers/__init__.py

@@ -14,9 +14,13 @@ def _envSolver(solver):
 
 solver = _envSolver(solver)
 
+class SerialSolverError(Exception):
+    def __init__(self, solver):
+        super(SerialSolverError, self).__init__(solver + ' does not run in parallel')
+
 if solver == "pysparse":
     if _parallel.Nproc > 1:
-        raise  Exception('pysparse solvers do not run in parallel')
+        raise SerialSolverError('pysparse')
     from fipy.solvers.pysparse import *
     __all__.extend(pysparse.__all__)
     from fipy.matrices.pysparseMatrix import _PysparseMeshMatrix
@@ -35,15 +39,15 @@ def _envSolver(solver):
 
 elif solver == "scipy":
     if _parallel.Nproc > 1:
-        raise  Exception('scipy solvers do not run in parallel')
+        raise SerialSolverError('scipy')
     from fipy.solvers.scipy import *
     __all__.extend(scipy.__all__)
     from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
     _MeshMatrix = _ScipyMeshMatrix
 
 elif solver == "pyamg":
     if _parallel.Nproc > 1:
-        raise  Exception('pyamg solvers do not run in parallel')
+        raise SerialSolverError('pyamg')
     from fipy.solvers.pyAMG import *
     __all__.extend(pyAMG.__all__)
     from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
@@ -58,18 +62,21 @@ def _envSolver(solver):
 elif solver is None:
     # If no argument or environment variable, try importing them and seeing
     # what works
-
 
-
+    exceptions = []
+
     try:
         if _parallel.Nproc > 1:
-            raise  Exception('pysparse solvers do not run in parallel')
+            raise SerialSolverError('pysparse solvers do not run in parallel')
         from fipy.solvers.pysparse import *
         __all__.extend(pysparse.__all__)
         solver = "pysparse"
         from fipy.matrices.pysparseMatrix import _PysparseMeshMatrix
         _MeshMatrix =  _PysparseMeshMatrix
-    except:
+
+    except (ImportError, SerialSolverError) as inst:
+        exceptions.append(inst)
+
         try:
             from fipy.solvers.trilinos import *
             __all__.extend(trilinos.__all__)
@@ -81,26 +88,36 @@ def _envSolver(solver):
                 solver = "no-pysparse"
                 from fipy.matrices.trilinosMatrix import _TrilinosMeshMatrix
                 _MeshMatrix =  _TrilinosMeshMatrix
-        except:
+        except ImportError as inst:
+            exceptions.append(inst)
+
             try:
                 if _parallel.Nproc > 1:
-                    raise  Exception('pyamg solvers do not run in parallel')
+                    raise SerialSolverError('pyamg')
                 from fipy.solvers.pyAMG import *
                 __all__.extend(pyAMG.__all__)
                 solver = "pyamg"
                 from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
                 _MeshMatrix = _ScipyMeshMatrix
-            except:
+            except (ImportError, SerialSolverError) as inst:
+                exceptions.append(inst)
+
                 try:
                     if _parallel.Nproc > 1:
-                        raise  Exception('scipy solvers do not run in parallel')
+                        raise SerialSolverError('scipy')
                     from fipy.solvers.scipy import *
                     __all__.extend(scipy.__all__)
                     solver = "scipy"
                     from fipy.matrices.scipyMatrix import _ScipyMeshMatrix
                     _MeshMatrix = _ScipyMeshMatrix
-                except:
-                    raise ImportError, "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." 
+                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
 

fipy/terms/asymmetricConvectionTerm.py

@@ -37,7 +37,7 @@
 __all__ = []
 
 from fipy.terms.abstractConvectionTerm import _AbstractConvectionTerm
-from fipy.solvers import DefaultAsymmetricSolver
+
 
 class _AsymmetricConvectionTerm(_AbstractConvectionTerm):
 
@@ -51,6 +51,7 @@ def _getDefaultSolver(self, var, solver, *args, **kwargs):
         if solver and not solver._canSolveAsymmetric():
             import warnings
             warnings.warn("%s cannot solve assymetric matrices" % solver)
+        from fipy.solvers import DefaultAsymmetricSolver
         return solver or DefaultAsymmetricSolver(*args, **kwargs)
 
 def _test(): 

fipy/terms/centralDiffConvectionTerm.py

@@ -38,7 +38,6 @@
 
 from fipy.terms.abstractConvectionTerm import _AbstractConvectionTerm
 from fipy.variables.faceVariable import FaceVariable
-from fipy.solvers import DefaultAsymmetricSolver
 
 __all__ = ["CentralDifferenceConvectionTerm"]
 

fipy/terms/term.py

@@ -37,7 +37,6 @@
 import os
 
 from fipy.tools import numerix
-from fipy.solvers import DefaultSolver, DummySolver
 from fipy.terms import AbstractBaseClassError
 from fipy.terms import SolutionVariableRequiredError
 from fipy.tools.decorators import getsetDeprecated
@@ -397,6 +396,7 @@ def _getDefaultSolver(self, var, solver, *args, **kwargs):
         return NotImplementedError
 
     def getDefaultSolver(self, var=None, solver=None, *args, **kwargs):
+        from fipy.solvers import DefaultSolver
         return solver or self._getDefaultSolver(var, solver, *args, **kwargs) or DefaultSolver(*args, **kwargs)
 
     def __add__(self, other):

fipy/terms/upwindConvectionTerm.py

@@ -37,7 +37,6 @@
 
 from fipy.terms.abstractUpwindConvectionTerm import _AbstractUpwindConvectionTerm
 from fipy.variables.faceVariable import FaceVariable
-from fipy.solvers import DefaultAsymmetricSolver
 
 __all__ = ["UpwindConvectionTerm"]
 
@@ -60,6 +59,7 @@ def _getDefaultSolver(self, var, solver, *args, **kwargs):
         if solver and not solver._canSolveAsymmetric():
             import warnings
             warnings.warn("%s cannot solve assymetric matrices" % solver)
+        from fipy.solvers import DefaultAsymmetricSolver
         return solver or DefaultAsymmetricSolver(*args, **kwargs)
 
     def _testPecletSign(self):