Exemple for get / set VertexMap inside c4d through python.

vertex_map_exemple.py

# coding: utf-8
"""
Exemple for get / set VertexMap inside c4d through python.
    Show an exemple of GetLowlevelDataAddressR / GetLowlevelDataAddressW
"""

__author__ = 'Adam Maxime - Graphos <gr4ph0s(at)hotmail.fr>'
__version__ = '1.0'


import c4d
import array

def vertex_map_to_list(vertex_map):
    # vertex_map => c4d.Tvertexmap

    buffer = vertex_map.GetLowlevelDataAddressR()
    if buffer is None: return None

    floatArray = array.array('f')
    floatArray.fromstring(buffer)
    weight_list = floatArray.tolist()

    return weight_list

def list_to_vertex_map(op, weight_list):
  # op => c4d.BaseObject or c4d.Tvertexmap
  # weight_list => list
    if not op: return None

    vertex_tag = None

    # if it's a baseObject we create a vertex_map
    if isinstance(op, c4d.BaseObject):
        vertex_tag = c4d.VariableTag(c4d.Tvertexmap, op.GetPointCount())
        op.InsertTag(vertex_tag)
    else:
        vertex_tag = op

    # Check the list filled into the function get correct point number
    if len(weight_list) != vertex_tag.GetDataCount(): return None

    # Get the write buffer array
    buffer = vertex_tag.GetLowlevelDataAddressW()
    if buffer is None: return None

    # Transle list to float array
    floatArray = array.array('f')
    floatArray.fromlist(weight_list)
    data = floatArray.tostring()
    buffer[:len(data)] = data

    return True

def set_pt_weight(vertex_map, pt_id, pt_weight):
  # vertex_map => c4d.Tvertexmap
  # pt_id => int
  # pt_weight => float
    if not vertex_map: return None

    # Check the pt_id filled is correct
    if pt_id > vertex_map.GetDataCount() or pt_id < 0: return None

    # Get the write buffer array
    buffer = vertex_map.GetLowlevelDataAddressW()
    if buffer is None: return None

    # Translate float into Bytseq float
    floatArray = array.array('f')
    floatArray.append(pt_weight)
    data = floatArray.tostring()

    # float get a size of 4. Since pt_id are ordered we just have to make pt_id*4 to get the start of the array
    buffer[pt_id*4: pt_id*4+4] = data

    return True

def main():
    # Get User data
    vertex_map = op[c4d.ID_USERDATA, 1]
    
    # Check if filled data are valid
    if not vertex_map: return
    if not vertex_map.CheckType(c4d.Tvertexmap): return

    # Get all the weight
    weight_list = vertex_map_to_list(vertex_map)

    # Change value inside the list
    for i, value in enumerate(weight_list):
        weight_list[i] = 0.75

    # Set all the weights with the previous modification of the list
    list_to_vertex_map(vertex_map, weight_list)

    # Set the weight of a particular pt_id
    set_pt_weight(vertex_map, 0, 0.25)

    c4d.EventAdd()

Thanks for this. I found it really helpful!