How to use the plyfile.PlyElement.describe function in plyfile

def test_assign_elements(tet_ply_txt):
    test = PlyElement.describe(numpy.zeros(1, dtype=[('a', 'i4')]),
                               'test')
    tet_ply_txt.elements = [test]
    assert len(tet_ply_txt.elements) == 1
    assert len(tet_ply_txt) == 1
    assert 'vertex' not in tet_ply_txt
    assert 'face' not in tet_ply_txt
    assert 'test' in tet_ply_txt

    for (k, elt) in enumerate(tet_ply_txt):
        assert elt.name == 'test'
        assert k == 0

'''

  import voxel_globe.tools
  with voxel_globe.tools.storage_dir('event_trigger_ply') as ply_dir:
    num_files = len([name for name in os.listdir(ply_dir)])
    filepath = os.path.join(ply_dir, 'mesh_%d.ply' % num_files)
  
  import numpy
  import plyfile
  from plyfile import PlyData, PlyElement
  
  vertex = numpy.array(points,
                      dtype=[('x', 'double'), ('y', 'double'),
                             ('z', 'double')])
  face = numpy.array([(range(len(points)),)], [('vertex_indices', '|O')])
  el1 = PlyElement.describe(vertex, 'vertex')
  el2 = PlyElement.describe(face, 'face')
  
  PlyData([el1, el2], text=True, comments=['mesh-feature'], 
    obj_info=['a bmsh3d_mesh object']).write(filepath)

  return filepath

desc = desc + vertex_color.dtype.descr

    vertex_all = np.empty(n, dtype=desc)

    for prop in vertex.dtype.names:
        vertex_all[prop] = vertex[prop]

    if normals is not None:
        for prop in vertex_normal.dtype.names:
            vertex_all[prop] = vertex_normal[prop]

    if colors is not None:
        for prop in vertex_color.dtype.names:
            vertex_all[prop] = vertex_color[prop]

    ply = plyfile.PlyData([plyfile.PlyElement.describe(vertex_all, 'vertex')], text=False)
    if not os.path.exists(os.path.dirname(filename)):
        os.makedirs(os.path.dirname(filename))
    ply.write(filename)

(-pointr1[2]*2/3, pointr1[0]*2/3, -pointr1[1]*2/3),
                  (-pointo1[2]*2/3, pointo1[0]*2/3, -pointo1[1]*2/3),
                  (((-pointt1[2]*2/3)+(-pointr1[2]*2/3)+(-pointo1[2]*2/3))/3 - 0.001,((pointt1[0]*2/3)+(pointr1[0]*2/3)+(pointo1[0]*2/3))/3,((-pointt1[1]*2/3)+(-pointr1[1]*2/3)+(-pointo1[1]*2/3))/3)],
                 dtype=[('x', 'f4'), ('y', 'f4'), ('z', 'f4')])

    face6 = np.array([([0, 1, 2], 0, 0, 0),#black face
                ([0, 2, 3], 0,   255,   255),
                ([0, 1, 3],   255, 0,   0),
                ([1, 2, 3],   255,   140, 0)],
               dtype=[('vertex_indices', 'i4', (3,)),
                      ('red', 'u1'), ('green', 'u1'),
                      ('blue', 'u1')])

    # Saves Point Cloud files under the given names (I have been changing it every time I want to make a new set of Point Clouds, otherwise it overwrites the previous file with the same name)
    PlyData([PlyElement.describe(vertex1, 'vertex'),PlyElement.describe(face1, 'face')]).write(bone1FileName)
    PlyData([PlyElement.describe(vertex2, 'vertex'),PlyElement.describe(face2, 'face')]).write(bone2FileName)
    PlyData([PlyElement.describe(vertex3, 'vertex'),PlyElement.describe(face3, 'face')]).write(bone3FileName)
    PlyData([PlyElement.describe(vertex4, 'vertex'),PlyElement.describe(face4, 'face')]).write(bone4FileName)
    PlyData([PlyElement.describe(vertex5, 'vertex'),PlyElement.describe(face5, 'face')]).write(bone5FileName)
    PlyData([PlyElement.describe(vertex6, 'vertex'),PlyElement.describe(face6, 'face')]).write(bone6FileName)

vertex6 = np.array([(-pointt1[2]*2/3, pointt1[0]*2/3, -pointt1[1]*2/3),
                  (-pointr1[2]*2/3, pointr1[0]*2/3, -pointr1[1]*2/3),
                  (-pointo1[2]*2/3, pointo1[0]*2/3, -pointo1[1]*2/3),
                  (((-pointt1[2]*2/3)+(-pointr1[2]*2/3)+(-pointo1[2]*2/3))/3 - 0.001,((pointt1[0]*2/3)+(pointr1[0]*2/3)+(pointo1[0]*2/3))/3,((-pointt1[1]*2/3)+(-pointr1[1]*2/3)+(-pointo1[1]*2/3))/3)],
                 dtype=[('x', 'f4'), ('y', 'f4'), ('z', 'f4')])

    face6 = np.array([([0, 1, 2], 0, 0, 0),#black face
                ([0, 2, 3], 0,   255,   255),
                ([0, 1, 3],   255, 0,   0),
                ([1, 2, 3],   255,   140, 0)],
               dtype=[('vertex_indices', 'i4', (3,)),
                      ('red', 'u1'), ('green', 'u1'),
                      ('blue', 'u1')])

    # Saves Point Cloud files under the given names (I have been changing it every time I want to make a new set of Point Clouds, otherwise it overwrites the previous file with the same name)
    PlyData([PlyElement.describe(vertex1, 'vertex'),PlyElement.describe(face1, 'face')]).write(bone1FileName)
    PlyData([PlyElement.describe(vertex2, 'vertex'),PlyElement.describe(face2, 'face')]).write(bone2FileName)
    PlyData([PlyElement.describe(vertex3, 'vertex'),PlyElement.describe(face3, 'face')]).write(bone3FileName)
    PlyData([PlyElement.describe(vertex4, 'vertex'),PlyElement.describe(face4, 'face')]).write(bone4FileName)
    PlyData([PlyElement.describe(vertex5, 'vertex'),PlyElement.describe(face5, 'face')]).write(bone5FileName)
    PlyData([PlyElement.describe(vertex6, 'vertex'),PlyElement.describe(face6, 'face')]).write(bone6FileName)

vertex6 = np.array([(-pointt1[2]*2/3, pointt1[0]*2/3, -pointt1[1]*2/3),
                  (-pointr1[2]*2/3, pointr1[0]*2/3, -pointr1[1]*2/3),
                  (-pointo1[2]*2/3, pointo1[0]*2/3, -pointo1[1]*2/3),
                  (((-pointt1[2]*2/3)+(-pointr1[2]*2/3)+(-pointo1[2]*2/3))/3 - 0.001,((pointt1[0]*2/3)+(pointr1[0]*2/3)+(pointo1[0]*2/3))/3,((-pointt1[1]*2/3)+(-pointr1[1]*2/3)+(-pointo1[1]*2/3))/3)],
                 dtype=[('x', 'f4'), ('y', 'f4'), ('z', 'f4')])

    face6 = np.array([([0, 1, 2], 0, 0, 0),#black face
                ([0, 2, 3], 0,   255,   255),
                ([0, 1, 3],   255, 0,   0),
                ([1, 2, 3],   255,   140, 0)],
               dtype=[('vertex_indices', 'i4', (3,)),
                      ('red', 'u1'), ('green', 'u1'),
                      ('blue', 'u1')])

    # Saves Point Cloud files under the given names (I have been changing it every time I want to make a new set of Point Clouds, otherwise it overwrites the previous file with the same name)
    PlyData([PlyElement.describe(vertex1, 'vertex'),PlyElement.describe(face1, 'face')]).write(bone1FileName)
    PlyData([PlyElement.describe(vertex2, 'vertex'),PlyElement.describe(face2, 'face')]).write(bone2FileName)
    PlyData([PlyElement.describe(vertex3, 'vertex'),PlyElement.describe(face3, 'face')]).write(bone3FileName)
    PlyData([PlyElement.describe(vertex4, 'vertex'),PlyElement.describe(face4, 'face')]).write(bone4FileName)
    PlyData([PlyElement.describe(vertex5, 'vertex'),PlyElement.describe(face5, 'face')]).write(bone5FileName)
    PlyData([PlyElement.describe(vertex6, 'vertex'),PlyElement.describe(face6, 'face')]).write(bone6FileName)

def write_ply(filename, xyz, rgb):
    """write into a ply file"""
    prop = [('x', 'f4'), ('y', 'f4'), ('z', 'f4'), ('red', 'u1'), ('green', 'u1'), ('blue', 'u1')]
    vertex_all = np.empty(len(xyz), dtype=prop)
    for i_prop in range(0, 3):
        vertex_all[prop[i_prop][0]] = xyz[:, i_prop]
    for i_prop in range(0, 3):
        vertex_all[prop[i_prop+3][0]] = rgb[:, i_prop]
    ply = PlyData([PlyElement.describe(vertex_all, 'vertex')], text=True)
    ply.write(filename)
#------------------------------------------------------------------------------

else:
    if points_3d.shape[1] == 3:
      gray_concat = np.tile(np.array([128], dtype=np.uint8), (points_3d.shape[0], 3))
      points_3d = np.hstack((points_3d, gray_concat))
    assert points_3d.shape[1] == 6
    python_types = (float, float, float, int, int, int)
    npy_types = [('x', 'f4'), ('y', 'f4'), ('z', 'f4'), ('red', 'u1'), ('green', 'u1'),
                 ('blue', 'u1')]
  if binary is True:
    # Format into NumPy structured array
    vertices = []
    for row_idx in range(points_3d.shape[0]):
      cur_point = points_3d[row_idx]
      vertices.append(tuple(dtype(point) for dtype, point in zip(python_types, cur_point)))
    vertices_array = np.array(vertices, dtype=npy_types)
    el = PlyElement.describe(vertices_array, 'vertex')

    # Write
    PlyData([el]).write(filename)
  else:
    # PlyData([el], text=True).write(filename)
    with open(filename, 'w') as f:
      f.write('ply\n'
              'format ascii 1.0\n'
              'element vertex %d\n'
              'property float x\n'
              'property float y\n'
              'property float z\n'
              'property uchar red\n'
              'property uchar green\n'
              'property uchar blue\n'
              'property uchar alpha\n'