In maya get all zero or near zero face vertex normals of a mesh using Python

maya_get_all_zero_normals.py

import maya.api.OpenMaya as om
from maya import cmds


def get_dag_path(name):
    """Return MDagPath from object name"""
    sel = om.MSelectionList()
    sel.add(name)
    return sel.getDagPath(0)


def get_mesh_zero_normals(mesh, tolerance=1e-10):
    """Return mesh face vertices of which the normal is zero.
    
    Args:
        mesh (str): Name of mesh node.
        tolerance (float): Tolerance for zero comparison.
        
    Returns:
        list: Individual .vtxFace components which have zero
              normal vectors
    """
    
    dag = get_dag_path(mesh)
    it = om.MItMeshFaceVertex(dag)
    
    result = om.MSelectionList()
    while not it.isDone():
    
        normal = it.getNormal()
        if normal.isEquivalent(om.MVector.kZeroVector, tolerance):
            # Zero or near zero normal detected
            result.add((dag, it.currentItem()))
    
        it.next()
        
    return list(result.getSelectionStrings())


if __name__ == "__main__":
    # Example with all normals zero
    transform, construction_history = cmds.polyCube()
    mesh = cmds.listRelatives(transform, type="mesh", fullPath=True)[0]
    cmds.polyNormalPerVertex(mesh, normalXYZ=[0, 0, 0])
    zero_normal_components = get_mesh_zero_normals(mesh)
    print(zero_normal_components)

    # Example with a single face vertex normal zero
    transform, construction_history = cmds.polyCube()
    mesh = cmds.listRelatives(transform, type="mesh", fullPath=True)[0]
    cmds.polyNormalPerVertex(mesh + ".vtxFace[0][0]", normalXYZ=[0, 0, 0])
    zero_normal_components = get_mesh_zero_normals(mesh)
    print(zero_normal_components)