Help: Selecting mesh vertices through the Python 2.0 API

[ejcarroll007]

Hey everyone,

I'm trying to figure out how to select vertices through the Maya Python 2.0 API, instead of using the maya.cmds. I'm testing to see how much of a performance boost I can get when using the API.

Example of how I would normally approach selecting vertices in maya.cmds

import maya.cmds as cmds

vertices = [0, 1, 2, 3, 4]

vertex_select_list = []    
for vertex in vertices:
    vertex_select_list.append("{0}.vtx[{1}]".format('pSphere1', vertex))
    
cmds.select(vertex_select_list)

Sample of my Python 2.0 API code for trying to select vertices. (This is what I scrounged up from how the internet does it)

import maya.api.OpenMaya as omapi2

vertices = [0, 1, 2, 3, 4]

sel = omapi2.MSelectionList()
sel.add("pSphere1")
dag, mObject = sel.getComponent(0)
mfn_components = omapi2.MFnSingleIndexedComponent(mObject)
mfn_object = mfn_components.create(omapi2.MFn.kMeshVertComponent)
mfn_components.addElements(vertices)
selection_list = omapi2.MSelectionList()
selection_list.add(mfn_object)
omapi2.MGlobal.setActiveSelectionList(selection_list)

The above code does not work as I get the following error...

# Error: RuntimeError: file <maya console> line 12: (kInvalidParameter): Object is incompatible with this method #

My 2 questions...

1. In the error above, I get an incompatible error. But I'm not exactly sure what the issue is, as the MSelectionList.add() method requires an MObject. Which I am passing through when I used the MFnSingleIndexedComponent.create() method. Does anyone why I'm getting this error and what it means exactly?
2. Is their a better/different way of selecting vertices through the Maya Python 2.0 API? I don't even know if this is the intended way of doing so.

Thanks,

-Eric

[stuzzz]

from maya.OpenMaya import * #import in this space for better visualisation

mesh = "pSphere1" 
vertices = MIntArray()
indices = [4,2,1]
[vertices.append(x) for x in indices] #there might be a better solution for initializing a MIntArray with an tuple. 

comp = MFnSingleIndexedComponent()
compObj = comp.create(MFn.kMeshVertComponent)
comp.addElements(vertices)

# we query the MDagPath of the mesh
dag = MDagPath()
sel = MSelectionList()
sel.add(mesh)
sel.getDagPath(0, dag) 

# we then include a MSelection with the dag and its component(MObject)
sel2 = MSelectionList()
sel2.add(dag, compObj)
MGlobal.setActiveSelectionList(sel2)

[stuzzz]

To Answer your questions:

1. The MObject you pass to the MSelectionList is a component type. MSelectionList::add expect a MObject of kMesh type (since you deal with mesh)
2. You might have a great reason for selecting vertices with the api. I'm not sure there's a better way. As you can see you can use MObject as container for a selection. If you need to deal with such objects just attach them to some class functions (i.e MFnMesh, MItGeometry) instead.

[ejcarroll007 · Accepted solution]

Hello stuzz,

Thank you for the demonstration with the Python 1.0 API, it works great. But I was looking for the 2.0 haha

But it did help me find out what my issue was and it's a slight difference in the MSelection.add()

When I was looking at the documentation, I thought I couldn't add more than 1 argument. I had missed that I could add a tuple (MDagPath, MObject))

So modifying it like this now works!

import maya.api.OpenMaya as omapi2

vertices = [0, 1, 2, 3, 4]

sel = omapi2.MSelectionList()
sel.add("pSphere1")
dag, mObject = sel.getComponent(0)
mfn_components = omapi2.MFnSingleIndexedComponent(mObject)
mfn_object = mfn_components.create(omapi2.MFn.kMeshVertComponent)
mfn_components.addElements(vertices)
selection_list = omapi2.MSelectionList()
selection_list.add((dag, mfn_object))
omapi2.MGlobal.setActiveSelectionList(selection_list)

Thanks for the help!

-Eric

[stuzzz]

I'm glad it helped