Accelerator __getitem__ generates strange behavior

If the_ring is an Accelerator object,

the_ring = sirius.SI_V07.create_accelerator()

then

the_ring[[0]][0] 

generates strange behavior.

[fernandohds564]

which strange behavior? in my case, the first time I tried this I got an UnicodeDecodeError
but in the subsequent times this happened:

In [102]: acc = sirius.SI_V10.create_accelerator()

In [103]: acc[[0]][0]
Out[103]: fam_name: 0

Either way, I think getitem is incomplete. We should have protection against this kind of mistyping. I think this would suffice:

elif isinstance(index, (list,tuple)) and len(index)>0 and isinstance(index[0],int):

what do you think, @afonsoharuo?

In principle, I believe this should be valid syntax. When you pass a list or tuple as indices to an Accelerator object, the expected return is another Accelerator object, with only the elements specified by the indices. The use of this syntax should return the first element of the Accelerator composed by only the fist element of the_ring.

[fernandohds564]

I understand. I thought that the index being passed in that case, ring[[0]] was a list of lists, but it is a list of integers. However we are not protected against ring[[[0]]] or something like that.

Regarding the bug reported, at home I got as I described before, but at work I get segmentation fault.
I don't know what is causing this.
@afonsoharuo

@fernandohds564, we can add an exception to the ring[[[0]]] case; the error I get with ring[[0]] is different sometimes.

Added exception.