# Buggy code
def __init__(
    self,
    filename,
    dataset_type="openPMD",
    storage_filename=None,
    units_override=None,
    unit_system="mks",
    **kwargs,
):
    self._handle = HDF5FileHandler(filename)
    self.gridsize = kwargs.pop("open_pmd_virtual_gridsize", 10**9)
    self._set_paths(self._handle, path.dirname(filename))
    Dataset.__init__(
        self,
        filename,
        dataset_type,
        units_override=units_override,
        unit_system=unit_system,
    )
    self.storage_filename = storage_filename
    self.fluid_types += ("openPMD",)
    particles = tuple(
        str(c) for c in self._handle[self.base_path + self.particles_path].keys()
    )
    if len(particles) > 1:
        # Only use on-disk particle names if there is more than one species
        self.particle_types = particles
    mylog.debug("open_pmd - self.particle_types: {}".format(self.particle_types))
    self.particle_types_raw = self.particle_types
    self.particle_types = tuple(self.particle_types)


# Traceback (KeyError)
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-6-606762cc9ee1> in <module>()
----> 1 yt.load('./example-ptcl/hdf5/data00000400.h5')

~/miniconda3/lib/python3.6/site-packages/yt/convenience.py in load(*args, **kwargs)
84     candidates = find_lowest_subclasses(candidates)
85     if len(candidates) == 1:
---> 86         return candidates[0](*args, **kwargs)
87     if len(candidates) == 0:
88         if ytcfg.get("yt", "enzo_db") != '' \

~/miniconda3/lib/python3.6/site-packages/yt/frontends/open_pmd/data_structures.py in __init__(self, filename, dataset_type, storage_filename, units_override, unit_system, **kwargs)
385         self.storage_filename = storage_filename
386         self.fluid_types += ("openPMD",)
--> 387         particles = tuple(str(c) for c in self._handle[self.base_path + self.particles_path].keys())
388         if len(particles) > 1:
389             # Only use on-disk particle names if there is more than one species

~/miniconda3/lib/python3.6/site-packages/yt/utilities/file_handler.py in __getitem__(self, key)
43
44     def __getitem__(self, key):
---> 45         return self.handle[key]
46
47     def __contains__(self, item):

h5py/_objects.pyx in h5py._objects.with_phil.wrapper (/Users/ilan/minonda/conda-bld/h5py_1496887972496/work/h5py/_objects.c:2846)()

h5py/_objects.pyx in h5py._objects.with_phil.wrapper (/Users/ilan/minonda/conda-bld/h5py_1496887972496/work/h5py/_objects.c:2804)()

~/miniconda3/lib/python3.6/site-packages/h5py/_hl/group.py in __getitem__(self, name)
167                 raise ValueError("Invalid HDF5 object reference")
168         else:
--> 169             oid = h5o.open(self.id, self._e(name), lapl=self._lapl)
170
171         otype = h5i.get_type(oid)

h5py/_objects.pyx in h5py._objects.with_phil.wrapper (/Users/ilan/minonda/conda-bld/h5py_1496887972496/work/h5py/_objects.c:2846)()

h5py/_objects.pyx in h5py._objects.with_phil.wrapper (/Users/ilan/minonda/conda-bld/h5py_1496887972496/work/h5py/_objects.c:2804)()

h5py/h5o.pyx in h5py.h5o.open (/Users/ilan/minonda/conda-bld/h5py_1496887972496/work/h5py/h5o.c:3740)()

KeyError: "Unable to open object (Object 'particles' doesn't exist)"

# Fixed code
def __init__(
    self,
    filename,
    dataset_type="openPMD",
    storage_filename=None,
    units_override=None,
    unit_system="mks",
    **kwargs,
):
    self._handle = HDF5FileHandler(filename)
    self.gridsize = kwargs.pop("open_pmd_virtual_gridsize", 10**9)
    self.standard_version = StrictVersion(self._handle.attrs["openPMD"].decode())
    self.iteration = kwargs.pop("iteration", None)
    self._set_paths(self._handle, path.dirname(filename), self.iteration)
    Dataset.__init__(
        self,
        filename,
        dataset_type,
        units_override=units_override,
        unit_system=unit_system,
    )
    self.storage_filename = storage_filename
    self.fluid_types += ("openPMD",)
    try:
        particles = tuple(
            str(c) for c in self._handle[self.base_path + self.particles_path].keys()
        )
        if len(particles) > 1:
            # Only use on-disk particle names if there is more than one species
            self.particle_types = particles
        mylog.debug("self.particle_types: {}".format(self.particle_types))
        self.particle_types_raw = self.particle_types
        self.particle_types = tuple(self.particle_types)
    except KeyError:
        pass