boxlib frontend does not work for pure hydro runs

[wolfram-schmidt]

Bug report

I spotted a problem with the boxlib/amrex frontend in the case of pure hydro runs. The problem is that the frontend by default expects particles. A while ago Mike Zingale fixed by putting if ("particles" in self.ds.parameters) before the read particle call, see https://bitbucket.org/yt_analysis/yt/pull-requests/2571/add-support-for-nyx-datasets-without/diff. Now, after compiling yt from the development branch and doing a test run with the latest Nyx/AMRex, it appears that this does not work any longer, as the error trace reports:

Code for reproduction

import yt
PATH = "/gfs1/work/hzfbhsws/DrivenTurbulence/test-omp4/"
ds = yt.load(PATH + "plt00461")
ds.field_list

Can provide data set or Nyx parameter files if required.

Actual outcome

--------------------------------------------------------------------------
FileNotFoundError                         Traceback (most recent call last)
<ipython-input-7-3fabb4ffc7bc> in <module>()
----> 1 ds.field_list

/home/b/hzfbhsws/yt-src/yt/data_objects/static_output.py in field_list(self)
    546     @property
    547     def field_list(self):
--> 548         return self.index.field_list
    549 
    550     def create_field_info(self):

/home/b/hzfbhsws/yt-src/yt/data_objects/static_output.py in index(self)
    504                 raise RuntimeError("You should not instantiate Dataset.")
    505             self._instantiated_index = self._index_class(
--> 506                 self, dataset_type=self.dataset_type)
    507             # Now we do things that we need an instantiated index for
    508             # ...first off, we create our field_info now.

/home/b/hzfbhsws/yt-src/yt/frontends/boxlib/data_structures.py in __init__(self, ds, dataset_type)
   1228 
   1229             self._read_particles("DM", is_checkpoint, 
-> 1230                                  nyx_extra_real_fields[0:self.ds.dimensionality+1])
   1231 
   1232 

/home/b/hzfbhsws/yt-src/yt/frontends/boxlib/data_structures.py in _read_particles(self, directory_name, is_checkpoint, extra_field_names)
    563 
    564     def _read_particles(self, directory_name, is_checkpoint, extra_field_names=None):
--> 565         pheader = self._determine_particle_output_type(directory_name)
    566         self.particle_headers[directory_name] = pheader(self.ds,
    567                                                         directory_name,

/home/b/hzfbhsws/yt-src/yt/frontends/boxlib/data_structures.py in _determine_particle_output_type(self, directory_name)
    555     def _determine_particle_output_type(self, directory_name):
    556         header_filename =  self.ds.output_dir + "/" + directory_name + "/Header"
--> 557         with open(header_filename, "r") as f:
    558             version_string = f.readline().strip()
    559             if version_string.startswith("Version_Two"):

FileNotFoundError: [Errno 2] No such file or directory: '/gfs1/work/hzfbhsws/DrivenTurbulence/test-omp4/plt00461/DM/Header'

Expected outcome

[('boxlib', 'MachNumber'),
 ('boxlib', 'Ne'),
 ('boxlib', 'Temp'),
 ('boxlib', 'density'),
 ('boxlib', 'forcex'),
 ('boxlib', 'forcey'),
 ('boxlib', 'forcez'),
 ('boxlib', 'magvort'),
 ('boxlib', 'rho_E'),
 ('boxlib', 'rho_e'),
 ('boxlib', 'xmom'),
 ('boxlib', 'ymom'),
 ('boxlib', 'zmom')]

Version Information

• Operating System: SuSE Linux Enterprise Server (SLES) version 11
• Python Version: 3.6
• yt version: master branch, commit f3ee5f3
• Other Libraries (if applicable):

Built from source using a conda environment.

[ngoldbaum]

This was fixed by #1950