list slicing seems disabled in python scripting

Question

I'm writting a small script for the script Node of animation nodes, which I suppose uses python 3.7 like my version of Blender 2.82 does, but I'm hitting a NotImplementedError when I try to slice a list.

Here's an example code that shows this

import math

#recieve v1 from Blender 

for i in range(len(v1) - 1): 
    p1 = v1[i]
    p2 = v1[i + 1]

    if (p1 - p2).length > maxDist:
        middleNode = ((p1.x+p2.x)/2,(p1.y+p2.y)/2,(p1.z+p2.z)/2)

        # v1[:i] = v1[0..i] and v1[i:] = v1[i..] 
        v1 = v1[:i] + middleNode + v1[i:] 
        #v1.insert(i+1,middleNode)

    i = i + 1

v2 = v1

# send back v2 to Blender

I'm currently finding a workaround around this, but I didnt know where to ask about this. I've only just started using python inside Blender and would be really disapointed if I couldnt use any kind of slicing.

Answer 1

So, Blender use Vector to describe all vector-like value in its own API, it is not only tuple but a well defined class with methods. Check the newest API here: Blender 2.80 API(or latest)

You will need to create Vector by yourself, don't wish Blender will get over-ridden parameter from tuples and other format:

So in your code:

middleNode = ((p1.x+p2.x)/2,(p1.y+p2.y)/2,(p1.z+p2.z)/2) # type: tuple(float,float,float)
v1 = v1[:i] + middleNode + v1[i:] # <---- this one won't work

Your are asking python to stick a list of Vector to a tuple, not even a list, it will break. You can actually list it like v1[:i] + [middleNode,] to make python think its OK. But, the list is not all Vector but a tuple inserted between your list:

Python allow you to put any data inside a list and tuple, even they are not all same type.

So you should make your middleNode = Vector((x,y,x)) and wrap it into a list and concat them like before.