Euler bug??

Coding Python Support
1

Hi All,

Any explanation / rationale for why the following happens would be greatly appreciated!!!


import Blender
from Blender import Mathutils
from Blender.Mathutils import *

X = Euler([0, 0, 0])
Y = X

print X, Y
    ######################
    ##gives
    #[0.0000, 0.0000, 0.0000]
    # [0.0000, 0.0000, 0.0000]
    ######################

Y[1] = 27

print X, Y
    ######################
    ##gives
    #[0.0000, 27.0000, 0.0000]
    # [0.0000, 27.0000, 0.0000]
    ######################

why are these two vars linked?!? Recursively, at that!

I have to do some sloppy code when attempting to snap an object to one rotation and back again. Sort of annoying, but may be sensical…I dunno.

2

BECAUSE THAT IS THE WAY PYTHON WORKS!!

it is not a problem with blender at all. When you assign objects [non-primitives … pretty much everything but int, float] they both point to the same object

some other fun things

a = range(2)
a[0] = a
print a
print a[0]

prints:
[[…], 1]
[[…], 1]

so a list can contain itself… good stuff

well anyway, the way you copy a list [but not the objects inside] is called a slice copy. Instead of Y = X do Y=X[:]

3

fair enough!

Thanks for the help!

4

If you want a copy of the object than you have to slice it.

>>> x = [[1,2,3],[4,5,6]]
>>> y= x[:]  #slice to obtain copy
>>> print y,x  
[[1, 2, 3], [4, 5, 6]] [[1, 2, 3], [4, 5, 6]]
>>> y[0] = 2
>>> print y,x
[2, [4, 5, 6]] [[1, 2, 3], [4, 5, 6]]
>>> y[1][1] = 9  #but note that this is the same object as x[1][1]
>>> print y,x
[2, [4, 9, 6]] [[1, 2, 3], [4, 9, 6]]
5

oh my!

That’s way confusing :-?

6

Not too confusing if you understand that the list [4,5,6] is the same object in x and y. So that changing elements of the list will change both x,y.

If you want a copy of everything in the list then python provides a deepcopy function. This will make a copy of everything.



>>> import copy
>>> x = [[1,2,3],[4,5,6]]
>>> y = copy.deepcopy(x)
>>> y[1][1] = 9
>>> print y,x
[[1, 2, 3], [4, 9, 6]] [[1, 2, 3], [4, 5, 6]]
>>>
7

starting to feel like an idiot…

but it appears that slicing and deepcopy can’t be applied to Eulers.


>>x = Euler([0,0,0])
>>y = x[:]

>>print x, y
[0.0000, 0.0000, 0.0000]
 [0.0, 0.0, 0.0]

>>y = copy.deepcopy(x)

Traceback (most recent call last):
  File "Text", line 14, in ?
  File "C:\PYTHON23\LIB\copy.py", line 220, in deepcopy
  raise Error(
copy.Error: un(deep)copyable object of type <type 'euler'>
8

I did not check this in 2.37a, but in cvs blender:

You can use the copy constructor to make a deep copy of an Euler:


x = Euler()
y = Euler( x )

Slicing an Euler yields a list, not an Euler.


x = Euler()
y = x[:]
print type(y), y