[yt-dev] Issue #850: ParticleTrajectories fails with weakly-referenced object no longer exists (yt_analysis/yt)

[Kacper Kowalik]

New issue 850: ParticleTrajectories fails with weakly-referenced object no longer exists
https://bitbucket.org/yt_analysis/yt/issue/850/particletrajectories-fails-with-weakly

Kacper Kowalik:

Following script:


```
#!python

from yt.analysis_modules.particle_trajectories.api import \
    ParticleTrajectories

my_fns = ["enzo_tiny_cosmology/DD%4.4i/DD%4.4i.hierarchy" %
          (i, i) for i in range(40)]
trajs = ParticleTrajectories(my_fns, [596])
```

fails with:

```
#!text
Traceback (most recent call last):
  File "bug.py", line 6, in <module>
    trajs = ParticleTrajectories(my_fns, [596])
  File "yt/analysis_modules/particle_trajectories/particle_trajectories.py", line 124, in __init__
    self._get_data(field)
  File "yt/analysis_modules/particle_trajectories/particle_trajectories.py", line 205, in _get_data
    fd = dd_first._determine_fields(field)[0]
  File "yt/data_objects/data_containers.py", line 464, in _determine_fields
    finfo = self.pf._get_field_info("unknown", fname)
ReferenceError: weakly-referenced object no longer exists
```

I'm currently on `1bf2d3688801 (yt-3.0) tip`