Heres the rundown:
This stuff will show up when the 2.3 blender python docs come out
Add a named and empty vertex (deform) group to the object this nmesh is
linked to. If this nmesh was newly created or accessed with GetRaw, it must first be linked to an object (with object.link or NMesh.PutRaw) so the method knows which object to update. This is because vertex groups in Blender are stored in the object -- not in the mesh, which may be linked to more than one object. For this reason, it's better to use "mesh = object.getData()" than "mesh = NMesh.GetRaw(meshName)" to access an existing mesh.
Remove a named vertex (deform) group from the object linked to this nmesh. All vertices assigned to the group will be removed (just from the group, not deleted from the mesh), if any. If this nmesh was newly created, it must first be linked to an object.
assignVertsToGroup(group, vertList, weight, assignmode = 'replace'):
Adds an array (a python list) of vertex points to a named vertex group associated with a mesh. The vertex list is a list of vertex indices from the mesh. You should assign vertex points to groups only when the mesh has all its vertex points added to it and is already linked to an object.
The example here adds a new set of vertex indices to a sphere primitive::
sphere = Blender.Object.Get('Sphere')
mesh = sphere.getData()
vertList = 
for x in range(300):
if x % 3 == 0:
mesh.assignVertsToGroup('firstGroup', vertList, 0.5, 'add')
removeVertsFromGroup(group, vertList = None):
Remove a list of vertices from the given group. If this nmesh was newly created, it must first be linked to an object.
getVertsFromGroup(group, weightsFlag = 0, vertList = None):
Return a list of vertex indices associated with the passed group. This method can be used to test whether a vertex index is part of a group and if so, what its weight is.
Append this to the example from assignVertsToGroup:
print "Vertex indices from group %s :" % groupName
print "Again, with weights:"
print "Again, with weights and restricted to the given indices:"