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:] 

    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.

  • $\begingroup$ What is the type of v1? In v1 = v1[:i] + middleNode + v1[i:]. You are asking python to concat list tuple list in that line $\endgroup$
    – HikariTW
    May 5 '20 at 1:25
  • $\begingroup$ v1 is a list of vectors fed through the animation node script node, I assumed the middleNode I defined was in the same format, isn't a vector list a list of tuples ? thanks for the lead ! $\endgroup$
    – Asymetr
    May 5 '20 at 1:29
  • $\begingroup$ Yeah.... I got your problem, let me answer it in answer format $\endgroup$
    – HikariTW
    May 5 '20 at 1:30
  • $\begingroup$ For your information, vectors have a to_tuple() method docs.blender.org/api/current/… $\endgroup$
    – Gorgious
    May 5 '20 at 6:43

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:

enter image description here

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:

enter image description here

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.

  • $\begingroup$ list.append() list.extend() will also do the work $\endgroup$
    – HikariTW
    May 5 '20 at 1:46
  • $\begingroup$ thanks a lot for the detailed answer ! that's certainly reassuring and great to know. So happy that this works and that I know more about how Blender handles things :DD $\endgroup$
    – Asymetr
    May 5 '20 at 2:19
  • $\begingroup$ Kindly recommend you to use Vector.lerp() function to do the middle node thing as described here $\endgroup$
    – HikariTW
    May 5 '20 at 6:25
  • $\begingroup$ I'm having a very hard time with Animation Nodes scripting tonight, every time I do Vector.lerp(n1, n2) the software says lerp() takes exactly2 arguments (1 given) and each time I try the other syntax like so n1.Vector.lerp(n2) it tells me the Vector object has no attribute Vector. SO Ive started hardcoding everything which is a real pain $\endgroup$
    – Asymetr
    May 5 '20 at 6:47
  • 1
    $\begingroup$ Assume you got two Vector n1 and n2 : middleNode = n1.lerp( n2, 0.5 ) 0.5 is to indicate how close lerp is going to adapt n2 value, between 0 and 1. So 0.5 mean middle of n1 and n2. Vector is a class, not an instance. Be aware of them $\endgroup$
    – HikariTW
    May 5 '20 at 6:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.