Finding Blendshape from Target Maya Python API

Question

I'm trying to find a blendshape deformer from a target mesh in the python maya api. I'm pretty sure I have to iterate through the dependency graph to get the blendshape.

This is what i'm trying:

import maya.OpenMaya as OpenMaya
import maya.OpenMayaAnim as OpenMayaAnim

#Name of our targetmesh.
targetMesh = "pSphere1"

#Add selection.
mSel = OpenMaya.MSelectionList()
mSel.add(targetMesh, True)

#Get MObj
mObj = OpenMaya.MObject()
mSel.getDependNode(0, mObj)

#Make iterator.
itDG = OpenMaya.MItDependencyGraph(mObj,
                                   OpenMaya.MFn.kBlendShape, 
                                   OpenMaya.MItDependencyGraph.kUpstream)

while not itDG.isDone():
    oCurrentItem = itDG.currentItem()
    blndSkin = OpenMayaAnim.MFnBlendShapeDeformer(oCurrentItem)
    print blndSkin
    break

Unfortunately I get no blendshape deformer.

The same example with maya.cmds:

import maya.cmds as cmds

targetMesh = "pSphere1"    

history = cmds.listHistory(targetMesh, future=True)
blndshape = cmds.ls(history, type="blendShape")

print blndshape

Any help would be greatly appreciated!

Answer 1

So here's the solution I got working i believe:

def getBlendShape(shape):
    '''
    @param Shape: Name of the shape node.
    Returns MFnBlendShapeDeformer node or None.
    '''
    # Create an MDagPath for our shape node:
    selList = OpenMaya.MSelectionList()
    selList.add(shape)
    mDagPath = OpenMaya.MDagPath()
    selList.getDagPath(0, mDagPath)

    #Create iterator.
    mItDependencyGraph = OpenMaya.MItDependencyGraph(
        mDagPath.node(),
        OpenMaya.MItDependencyGraph.kPlugLevel)

    # Start walking through our shape node's dependency graph.
    while not mItDependencyGraph.isDone():
        # Get an MObject for the current item in the graph.
        mObject = mItDependencyGraph.currentItem()
        # It has a BlendShape.
        if mObject.hasFn(OpenMaya.MFn.kBlendShape):
            # return the MFnSkinCluster object for our MObject:
            return OpenMayaAnim.MFnBlendShapeDeformer(mObject)
        mItDependencyGraph.next()

if __name__ == '__main__':
    #TargetMesh
    targetMesh = "pSphereShape1"

    #Get Blendshape.
    blndShpNode = getBlendShape(targetMesh)

    if blndShpNode:
        #Get base objects.
        mObjArr = OpenMaya.MObjectArray()
        blndShpNode.getBaseObjects(mObjArr)
        mDagPath = OpenMaya.MDagPath()
        OpenMaya.MFnDagNode(mObjArr[0]).getPath(mDagPath)
        print(mDagPath.fullPathName())

    else:
        print("No Blendshape found.")

The trick is that I needed to pass the shape node and to only use OpenMaya.MItDependencyGraph.kPlugLevel). In this example it finds the base object of the blendshape.