# Buggy code
def _get_particle_type_counts(self):
    """Reads the active number of particles for every species.

    Returns
    -------
    dict
        keys are ptypes
        values are integer counts of the ptype
    """
    result = {}
    f = self.dataset._handle
    bp = self.dataset.base_path
    pp = self.dataset.particles_path
    for ptype in self.ds.particle_types_raw:
        if str(ptype) == "io":
            spec = list(f[bp + pp].keys())[0]
        else:
            spec = ptype
        axis = list(f[bp + pp + "/" + spec + "/position"].keys())[0]
        pos = f[bp + pp + "/" + spec + "/position/" + axis]
        if is_const_component(pos):
            result[ptype] = pos.attrs["shape"]
        else:
            result[ptype] = pos.len()
    return result


# 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 _get_particle_type_counts(self):
    """Reads the active number of particles for every species.

    Returns
    -------
    dict
        keys are ptypes
        values are integer counts of the ptype
    """
    result = {}
    f = self.dataset._handle
    bp = self.dataset.base_path
    pp = self.dataset.particles_path

    try:
        for ptype in self.ds.particle_types_raw:
            if str(ptype) == "io":
                spec = list(f[bp + pp].keys())[0]
            else:
                spec = ptype
            axis = list(f[bp + pp + "/" + spec + "/position"].keys())[0]
            pos = f[bp + pp + "/" + spec + "/position/" + axis]
            if is_const_component(pos):
                result[ptype] = pos.attrs["shape"]
            else:
                result[ptype] = pos.len()
    except KeyError:
        result["io"] = 0

    return result