adding elements to list in between indexes while iterating over that list in python

Question

I'm trying to iterate over a list of 3D points and create a new point between each group of two points that has a distance larger than a constant value.

I've tried using a buffer unsuccesfully, my main problem is that each newly inserted point needs to respect list order and be inserted between the two points it is between geometrically.

import math

#recieve v1 and maxDist from Blender

buffer = v1
offset = 0

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)
        offset = offset + 1 # 
        buffer.insert(i + offset, middleNode)

v2 = buffer

# send back v2 to Blender

the output that I'm having right now ressembles this while a perfectly subdivided circle is expected

Allan Juan · Accepted Answer · 2020-05-05 00:57:19Z

2

Your solution can be simpler if you use a single list instead of two. My approach would be:

i = 0
while i < 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 += 2
    else:
        i += 1

Or if list comprehension is not an option:

i = 0
while i < len(v1) - 1:
    p1 = v1[i]
    p2 = v1[i]

    if (p1 - p2).length > maxDist:
        middleNode = ((p1.x+p2.x)/2,(p1.y+p2.y)/2,(p1.z+p2.z)/2)
        v1.insert(i + 1, middleNode)
        i += 2
    else:
        i += 1

edited May 5, 2020 at 0:57

answered May 5, 2020 at 0:01

Allan Juan

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4 Comments

Kaspie Over a year ago

damn, I get a NotImplmentedError for line 13 with the list comprehension. The python version that I'm using is the one inside Blender which is sometimes of a pain. Are they in a specific module or not ?

Allan Juan Over a year ago

Nope, this list comprehension is a native python operator, but I can't tell you in which version it was implemented. Apparently, yours doesn't support it. I'm going to edit it with a solution that doesn't use list comprehension, wait a bit.

Kaspie Over a year ago

thanks a lot ! works great perfectly, I added a fixId function also to get the last missing pair that is caused by the len(v1) - 1 and it all works like a charm

Allan Juan Over a year ago

Nice, I'm glad to help!

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