Revert "Changed gb settings to use strings rather than named constants."

This reverts commit 4572d2e3.

wrappers/python/simtk/openmm/app/amberprmtopfile.py

@@ -40,11 +40,11 @@ import simtk.unit as unit
 import simtk.openmm as mm
 
 # Enumerated values for implicit solvent model
-# Prefer to use strings now, but these are here for backwards compatibility
-HCT = 'HCT'
-OBC1 = 'OBC1'
-OBC2 = 'OBC2'
-GBn = 'GBn'
+
+HCT = object()
+OBC1 = object()
+OBC2 = object()
+GBn = object()
 
 class AmberPrmtopFile(object):
     """AmberPrmtopFile parses an AMBER prmtop file and constructs a Topology and (optionally) an OpenMM System from it."""
@@ -122,8 +122,7 @@ class AmberPrmtopFile(object):
          - constraints (object=None) Specifies which bonds angles should be implemented with constraints.
            Allowed values are None, HBonds, AllBonds, or HAngles.
          - rigidWater (boolean=True) If true, water molecules will be fully rigid regardless of the value passed for the constraints argument
-         - implicitSolvent (object=None) If not None, the implicit solvent
-           model to use.  Allowed values are 'HCT', 'OBC1', 'OBC2', or 'GBn'.
+         - implicitSolvent (object=None) If not None, the implicit solvent model to use.  Allowed values are HCT, OBC1, OBC2, or GBn.
          - soluteDielectric (float=1.0) The solute dielectric constant to use in the implicit solvent model.
          - solventDielectric (float=78.5) The solvent dielectric constant to use in the implicit solvent model.
          - removeCMMotion (boolean=True) If true, a CMMotionRemover will be added to the System
@@ -149,12 +148,21 @@ class AmberPrmtopFile(object):
             constraintString = constraintMap[constraints]
         else:
             raise ValueError('Illegal value for constraints')
-
-        sys = amber_file_parser.readAmberSystem(prmtop_loader=self._prmtop, shake=constraintString,
-                                                nonbondedCutoff=nonbondedCutoff, nonbondedMethod=methodMap[nonbondedMethod],
-                                                flexibleConstraints=False, gbmodel=implicitSolvent,
-                                                soluteDielectric=soluteDielectric, solventDielectric=solventDielectric,
-                                                rigidWater=rigidWater)
+        if implicitSolvent is None:
+            implicitString = None
+        elif implicitSolvent == HCT:
+            implicitString = 'HCT'
+        elif implicitSolvent == OBC1:
+            implicitString = 'OBC1'
+        elif implicitSolvent == OBC2:
+            implicitString = 'OBC2'
+        elif implicitSolvent == GBn:
+            implicitString = 'GBn'
+        else:
+            raise ValueError('Illegal value for implicit solvent model')
+        sys = amber_file_parser.readAmberSystem(prmtop_loader=self._prmtop, shake=constraintString, nonbondedCutoff=nonbondedCutoff,
+                                                 nonbondedMethod=methodMap[nonbondedMethod], flexibleConstraints=False, gbmodel=implicitString,
+                                                 soluteDielectric=soluteDielectric, solventDielectric=solventDielectric, rigidWater=rigidWater)
         for force in sys.getForces():
             if isinstance(force, mm.NonbondedForce):
                 force.setEwaldErrorTolerance(ewaldErrorTolerance)

wrappers/python/simtk/openmm/app/gromacstopfile.py

@@ -45,7 +45,7 @@ HBonds = ff.HBonds
 AllBonds = ff.AllBonds
 HAngles = ff.HAngles
 
-OBC2 = 'OBC2'
+OBC2 = prmtop.OBC2
 
 class GromacsTopFile(object):
     """GromacsTopFile parses a Gromacs top file and constructs a Topology and (optionally) an OpenMM System from it."""
@@ -426,7 +426,7 @@ class GromacsTopFile(object):
          - constraints (object=None) Specifies which bonds and angles should be implemented with constraints.
            Allowed values are None, HBonds, AllBonds, or HAngles.
          - rigidWater (boolean=True) If true, water molecules will be fully rigid regardless of the value passed for the constraints argument
-         - implicitSolvent (string=None) If not None, the implicit solvent model to use.  The only allowed value is 'OBC2'.
+         - implicitSolvent (object=None) If not None, the implicit solvent model to use.  The only allowed value is OBC2.
          - soluteDielectric (float=1.0) The solute dielectric constant to use in the implicit solvent model.
          - solventDielectric (float=78.5) The solvent dielectric constant to use in the implicit solvent model.
          - ewaldErrorTolerance (float=0.0005) The error tolerance to use if nonbondedMethod is Ewald or PME.
@@ -443,7 +443,7 @@ class GromacsTopFile(object):
             raise ValueError('Illegal nonbonded method for a non-periodic system')
         nb = mm.NonbondedForce()
         sys.addForce(nb)
-        if implicitSolvent == 'OBC2':
+        if implicitSolvent is OBC2:
             gb = mm.GBSAOBCForce()
             gb.setSoluteDielectric(soluteDielectric)
             gb.setSolventDielectric(solventDielectric)
@@ -656,7 +656,7 @@ class GromacsTopFile(object):
                     else:
                         q = float(params[3])
                     nb.addParticle(q, float(params[5]), float(params[6]))
-                    if implicitSolvent == 'OBC2':
+                    if implicitSolvent is OBC2:
                         if fields[1] not in self._implicitTypes:
                             raise ValueError('No implicit solvent parameters specified for atom type: '+fields[1])
                         gbparams = self._implicitTypes[fields[1]]