Metadata

User metadata

BLISS provides a global structure to associate names (string keys) to functions, which return values are inserted in the scan_info dictionary that contains metadata information for scans.

Depending on which writer is used for scans, the metadata information is then written at the appropriate place.

By default, BLISS is saving data in the HDF5 format, following Nexus convention.

Available categories are:

• instrument
• sample
• sample_description
• proposal
• technique

Filling metadata

The get_user_scan_meta() function from bliss.scanning.scan_meta returns the scan metadata object. Each metadata category is accessible via the corresponding property. Then, the .set() method allows to associate a name or an object with a .name property to a function, that has to return a dictionary to be stored as metadata for the object, for the category.

The following example adds the position label of a Multiple Position object under the ‘Instrument’ category to each scan metadata:

```python
from bliss.scanning import scan_meta

scan_meta_obj = scan_meta.get_user_scan_meta()

# mp is a BLISS Multiple Position object
scan_meta_obj.instrument.set(mp, lambda _: { "position_label": mp.position })
```

The function receives the scan object as argument. In the example above, this argument is ignored.

Each subsequent scan will have an ‘instrument’ section filled with the metadata: