If you want to look at the HDF5 file written by the Nexus writer during a scan, use silx or pymca. Do not use third-party tools or custom scripts that are not approved by the ESRF Data Analysis Unit. More details can be found here.
A reader should never open the HDF5 file in append mode (which is the default in
h5py). Even when only performing read operations, this will result in a corrupted file!
A reader which locks the HDF5 file (this happens by default, even in read-only mode) will prevent the Nexus writer from accessing the file and scans in BLISS will be prevented from starting!