[ase-users] Error when trying to ase.visualize.view atom with FixCartesian constraint

[Lorenzi, Juan]

Hi all,

I am getting an error when I try to view an atoms object in which I included a FixCartesian constraint. Here is a minimal example that reproduces this

#+BEGIN_SRC python
  import ase
  from ase.visualize import view
  from ase.constraints import FixCartesian

  atoms = ase.Atoms('CO',cell = [3.,3.,3.], positions = [[0.,0.,0.,],[0.,0.,1.,],])

  atoms.set_constraint(FixCartesian(a = 1, mask = (0,0,1)))

  view(atoms)
#+END_SRC

and traceback I get is

#+BEGIN

Traceback (most recent call last):
  File "<stdin>", line 13, in <module>
  File "<stdin>", line 11, in main
  File "/user/lorenzi/.local/lib/python2.7/site-packages/ase/visualize/__init__.py", line 48, in view
    write(filename, atoms, format=format)
  File "/user/lorenzi/.local/lib/python2.7/site-packages/ase/io/__init__.py", line 615, in write
    write(filename, images, **kwargs)
  File "/user/lorenzi/.local/lib/python2.7/site-packages/ase/io/trajectory.py", line 311, in write_trajectory
    trj.write(atoms)
  File "/user/lorenzi/.local/lib/python2.7/site-packages/ase/io/trajectory.py", line 132, in write
    self.write_header(atoms)
  File "/user/lorenzi/.local/lib/python2.7/site-packages/ase/io/trajectory.py", line 212, in write_header
    b.write(constraints=encode(atoms.constraints))
  File "/usr/lib/python2.7/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/lib/python2.7/json/encoder.py", line 263, in iterencode
    return _iterencode(o, 0)
  File "/user/lorenzi/.local/lib/python2.7/site-packages/ase/io/jsonio.py", line 18, in default
    return json.JSONEncoder.default(self, obj)
  File "/usr/lib/python2.7/json/encoder.py", line 177, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: FixCartesian(indice=1 mask=[1 1 0]) is not JSON serializable

#+END

Is this a problem with my installation or a bug? (or a feature?)

Thanks a lot for your help!

---
Juan M. Lorenzi
PhD Student
Theoretical Chemistry
Technical University of Munich (TUM)
Lichtenberstr. 4
D-85747 Garching, Germany
Tel: +49 89 289 13808, Room CH62108
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