Default extra particle identifier is the same for reading and writing

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

@@ -260,7 +260,7 @@ class PDBFile(object):
                 map[atom.attrib[id]] = name
 
     @staticmethod
-    def writeFile(topology, positions, file=sys.stdout, keepIds=False, extraParticleIdentifier=' '):
+    def writeFile(topology, positions, file=sys.stdout, keepIds=False, extraParticleIdentifier='EP'):
         """Write a PDB file containing a single model.
 
         Parameters
@@ -276,7 +276,7 @@ class PDBFile(object):
             rather than generating new ones.  Warning: It is up to the caller to
             make sure these are valid IDs that satisfy the requirements of the
             PDB format.  Otherwise, the output file will be invalid.
-        extraParticleIdentifier : string=' '
+        extraParticleIdentifier : string='EP'
             String to write in the element column of the ATOM records for atoms whose element is None (extra particles)
         """
         PDBFile.writeHeader(topology, file)
@@ -303,7 +303,7 @@ class PDBFile(object):
                     a*10, b*10, c*10, alpha*RAD_TO_DEG, beta*RAD_TO_DEG, gamma*RAD_TO_DEG), file=file)
 
     @staticmethod
-    def writeModel(topology, positions, file=sys.stdout, modelIndex=None, keepIds=False, extraParticleIdentifier=' '):
+    def writeModel(topology, positions, file=sys.stdout, modelIndex=None, keepIds=False, extraParticleIdentifier='EP'):
         """Write out a model to a PDB file.
 
         Parameters
@@ -323,7 +323,7 @@ class PDBFile(object):
             make sure these are valid IDs that satisfy the requirements of the
             PDB format.  No guarantees are made about what will happen if they
             are not, and the output file could be invalid.
-        extraParticleIdentifier : string=' '
+        extraParticleIdentifier : string='EP'
             String to write in the element column of the ATOM records for atoms whose element is None (extra particles)
         """