I am loading an existing halo catalog to create a DataSet object: import yt ds = yt.load("test_halo_catalog.h5") I then wish to use the all_data() method: ad = ds.all_data() But if the halo catalog contains zero halos, I get this error message: yt : [INFO ] 2024-04-26 14:06:04,162 Allocating for 0.000e+00 particles Traceback (most recent call last): File "~/hc_analysis.py", line 130, in <module> ad = ds.all_data() File "/home/hannah/anaconda3/envs/yt-rockstar/lib/python3.10/site-packages/yt/data_objects/static_output.py", line 1122, in all_data self.index File "/home/hannah/anaconda3/envs/yt-rockstar/lib/python3.10/site-packages/yt/data_objects/static_output.py", line 559, in index self._instantiated_index = self._index_class( File "/home/hannah/anaconda3/envs/yt-rockstar/lib/python3.10/site-packages/yt/geometry/particle_geometry_handler.py", line 27, in __init__ self._initialize_index() File "/home/hannah/anaconda3/envs/yt-rockstar/lib/python3.10/site-packages/yt/geometry/particle_geometry_handler.py", line 164, in _initialize_index self.regions = ParticleBitmap( File "yt/geometry/particle_oct_container.pyx", line 476, in yt.geometry.particle_oct_container.ParticleBitmap.__init__ TypeError: an integer is required It seems that all_data() only works if the halo catalog contains a nonzero integer number of halos. Is there a method for a DataSet object to determine the total number of halos found? I wish to implement something like this: if ds.total_halos != 0: ad = ds.all_data() else: print("No halos found in this halo catalog") Any help would be much appreciated, thank you! Kind regards, Hannah O'Brennan