Can't load biotite.structure.AtomArray after pickle.dump(...)

[entropybit]

Hi,

I encountered the problem that it does not seem possible to load a structure once it has been dumped using pickle.
That poses a a problem as you might want to have a AtomArray as a member in some object, for which you then have the exact same problem. A minimum example is :

import biotite.structure.io as strucio
import biotite.database.rcsb as rcsb
from tempfile import gettempdir
import pickle

file = rcsb.fetch("1l2y", "pdb",gettempdir())
struc = strucio.load_structure(file)
pickle.dump(struc, open("struc.pckl", "wb"))
struc2 = pickle.load(open("struc.pckl", "rb"))

which yields

Traceback (most recent call last):
  File "pickle_test.py", line 9, in <module>
    struc2 = pickle.load(open("struc.pckl", "rb"))
  File "/home/mayer/miniconda3_rdkit/lib/python3.7/site-packages/biotite/structure/atoms.py", line 268, in __getattr__
    elif attr in self._annot:
  File "/home/mayer/miniconda3_rdkit/lib/python3.7/site-packages/biotite/structure/atoms.py", line 268, in __getattr__
    elif attr in self._annot:
  File "/home/mayer/miniconda3_rdkit/lib/python3.7/site-packages/biotite/structure/atoms.py", line 268, in __getattr__
    elif attr in self._annot:
  [Previous line repeated 495 more times]
  File "/home/mayer/miniconda3_rdkit/lib/python3.7/site-packages/biotite/structure/atoms.py", line 262, in __getattr__
    if attr == "coord":
RecursionError: maximum recursion depth exceeded in comparison

EDIT:

As I also had problems with distribution of multiple structures via MPI I was going to write a simple test.
However, as I was to lazy to produce a list of structures I just tried to make a list made from copies of the already loaded structure. This yields the same error as above:

import biotite.structure.io as strucio
from tempfile import gettempdir
import biotite.database.rcsb as rcsb
import copy

file = rcsb.fetch("1l2y", "pdb",gettempdir())
struc = strucio.load_structure(file)
strucs = [copy.copy(struc) for i in range(20)]

[padix-key]

Thank you for the report. I created a PR to fix this issue.