collection iteration and renaming, output unpredictable results #107027

New Issue

bar · 2023-04-17T10:26:28+02:00

bar commented

2023-04-17 10:26:28 +02:00

System Information
Operating system: Linux-5.19.0-38-generic-x86_64-with-glibc2.35 64 Bits
Graphics card: NVIDIA GeForce RTX 3080 Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 515.105.01

Blender Version
Broken: version: 3.4.1, branch: blender-v3.4-release, commit date: 2022-12-19 17:00, hash: rB55485cb379f7
Worked: (newest version of Blender that worked as expected)

Short description of error
[Please fill out a short description of the error here]

collection iteration and renaming, output unpredictable results
please run the script with attached file and check the results.

this script suppose to rename all object with lower case and prefix.
unfortunately, after running the script on N number of objects the results are unpredictable

import bpy

prefix = "blender_is_great"
print("##########################")


if bpy.data.objects:
    for obj in bpy.data.objects: # workaround list(bpy.data.objects)
        print(obj)
       
        new_name = f"{prefix}_{obj.name.lower()}"
        obj.name = new_name

**System Information** Operating system: Linux-5.19.0-38-generic-x86_64-with-glibc2.35 64 Bits Graphics card: NVIDIA GeForce RTX 3080 Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 515.105.01 **Blender Version** Broken: version: 3.4.1, branch: blender-v3.4-release, commit date: 2022-12-19 17:00, hash: `rB55485cb379f7` Worked: (newest version of Blender that worked as expected) **Short description of error** [Please fill out a short description of the error here] collection iteration and renaming, output unpredictable results please run the script with attached file and check the results. this script suppose to rename all object with lower case and prefix. unfortunately, after running the script on N number of objects the results are unpredictable ------- ``` import bpy prefix = "blender_is_great" print("##########################") if bpy.data.objects: for obj in bpy.data.objects: # workaround list(bpy.data.objects) print(obj) new_name = f"{prefix}_{obj.name.lower()}" obj.name = new_name ```

bug_naming.blend

169 KiB

bar added the

labels 2023-04-17 10:26:28 +02:00

YimingWu commented

2023-04-17 10:37:44 +02:00

Hi @barakooda , there's a name length limit to all ID data blocks (64 characters). That's why when your prefix gets too long, they will get truncated (if that's what you are referring to as "unpredictable").

bar commented

2023-04-17 10:54:34 +02:00

Hi @ChengduLittleA
no just run the code and check this image for reference:

do you see the unwanted repeating ?

Hi @ChengduLittleA no just run the code and check this image for reference: do you see the unwanted repeating ? ![image](/attachments/52e80c10-ec4a-45a8-ade5-7cbc67d73b05)

image.png

330 KiB

YimingWu commented

2023-04-17 11:15:56 +02:00

@barakooda Looks that's what exactly what your script does?

bar commented

2023-04-17 11:42:54 +02:00

@ChengduLittleA

no,
the script adds the prefix only a single time.

@ChengduLittleA no, the script adds the prefix only a single time.

YimingWu commented

2023-04-17 13:12:04 +02:00

Hi @barakooda , I can confirm that's indeed what's happening. I think I know the reason why the script is doing it in such a way. When you change the name of an object, blender will sort the object list, so bpy.data.objects would change. By naming stuff this way, you will potentially iterate over the same object because the list order changed.

Instead, you could use for ob in bpy.data.objects.values(), this way it preserves the list order and you only iterate over objects once.

Hi @barakooda , I can confirm that's indeed what's happening. I think I know the reason why the script is doing it in such a way. When you change the name of an object, blender will sort the object list, so `bpy.data.objects` would change. By naming stuff this way, you will potentially iterate over the same object because the list order changed. Instead, you could use `for ob in bpy.data.objects.values()`, this way it preserves the list order and you only iterate over objects once.

👍 1

Philipp Oeser commented

2023-04-21 11:37:44 +02:00

This is sort of touched by https://docs.blender.org/api/3.6/info_gotcha.html

Closest to it is here:

This could be more explicit, but I do think this is the same ballpark.

@ideasman42 , @sergey : would you agree?

This is sort of touched by https://docs.blender.org/api/3.6/info_gotcha.html Closest to it is here: - https://docs.blender.org/api/3.6/info_gotcha.html#help-my-script-crashes-blender - https://docs.blender.org/api/3.6/info_gotcha.html#unfortunate-corner-cases This could be more explicit, but I do think this is the same ballpark. @ideasman42 , @sergey : would you agree?

Philipp Oeser added

Module

Python API

Status

Needs Info from Developers

and removed

Status

Needs Triage

labels 2023-04-21 11:38:06 +02:00

Sergey Sharybin commented

2023-04-21 12:00:17 +02:00

Indeed. Maybe can have a bullet point of common cases (without giving full-blown code snippet) ?