The Arguments class provides a flexible way to store any argument that need to be passed to functions or classes. Other pipeline frameworks have adopted a well-defined data model, using arrays or more sophisticated data structures to store FITS files or tables.

For this framework, we have opted for the maximum flexibility.

A very simple argument can be built by using just the file name:

from keckdrpframework.models.arguments import Arguments
file_name = 'kb01.fits'
arguments = Arguments(name=file_name)

This argument can then be used to add an event to the processing queue:

framework.append_event('my_code', arguments)

The argument class can be extended with any type of Python object using the syntax argument.<object. An example of using this concept is the way that we process the Keck Cosmic Web Imager (KCWI) data. For this instrument, the raw FITS file is made of two extensions: the actual CCD data and a table listing the shutter open/close events with timestamps.

To read this type of FITS files, we can define a specific FITS reader for KCWI as:

def kcwi_fits_reader(file):
    """A reader for KeckData objects.
    hdul =

    if len(hdul) == 2:
        # 1- read the first extension into a ccddata
        ccddata = CCDData(hdul[0].data, meta=hdul[0].header, unit='adu')
        # 2- read the table
        table = hdul[1]

    return ccddata, table

We can then create a primitive that can take care of ingesting a KCWI FITS file by subclassing the Base_primitive as described in the previous section (see primitives_):

class kcwi_fits_ingest(Base_primitive):

    def __init__(self, action, context):
        Base_primitive.__init__(self, action, context)

    def _perform(self):
        Expects as fits file name
        Returns HDUs or (later) data model
        name ="Reading {name}")
        out_args = Arguments() = name
        ccddata, table = self.kcwi_fits_reader(name)
        out_args.ccddata = ccddata
        out_args.table = table
        out_args.imtype = out_args.hdus.header['IMTYPE']

     return out_args

Note that the name of the file is passed to this function as part of the action dictionary. We will describe this dictionary later. The relevant code is the construction of the out_args variable: first, it is instantiated as Arguments, then it is populated with various elements such as an Astropy NDData CCDData object for the CCD data, and a table. Finally, and just for convenience, the image type is extracted from the header and assigned to the imtype property of the class. Any other property can be added to the arguments.

By doing this, we have effectively defined our own KCWI data model as being composed of a CCDData object, plus a table, plus additional extracted information such as the image type.