WriteTriangleToFile

import vtk

Points = vtk.vtkPoints()
Triangles = vtk.vtkCellArray()
Triangle = vtk.vtkTriangle()

id = Points.InsertNextPoint(1.0, 0.0, 0.0)
id = Points.InsertNextPoint(0.0, 0.0, 0.0)
id = Points.InsertNextPoint(0.0, 1.0, 0.0)

Triangle.GetPointIds().SetId(0, 0)
Triangle.GetPointIds().SetId(1, 1)
Triangle.GetPointIds().SetId(2, 2)
Triangles.InsertNextCell(Triangle)


polydata = vtk.vtkPolyData()
polydata.SetPoints(Points)
polydata.SetPolys(Triangles)
polydata.Modified()
if vtk.VTK_MAJOR_VERSION <= 5:
    polydata.Update()

writer = vtk.vtkXMLPolyDataWriter()
writer.SetFileName("Triangle.vtp")
if vtk.VTK_MAJOR_VERSION <= 5:
    writer.SetInput(polydata)
else:
    writer.SetInputData(polydata)
writer.Write()