3. Configuring slitlessutils

Many of the functions and classes within slitlessutils expose their individual default settings, however in some cases it is important to define global variables that govern calibration files or large-scale aspects of the package. Consequently, slitlessutils establishes these settings in a singleton class Config() that generally acts like a standard Python dictionary.

3.1. Slitlessutils Calibration Files

The reference files used to perform the spectral extraction and modeling with slitlessutils must be installed in a dot-directory in the user’s home: {$HOME}/.slitlessutils. When the Config() object is instantiated, it will check if this directory exists and valid reference files are populated. If no such directory is found, then it is created; if no such reference files are found, then the most recent files will be automatically retrieved from a public box directory. However, users can programmatically retrieve and use older versions of files:

# load the config module
from slitlessutils import config
cfg = config.Config()

# download the latest reference files
reffile = cfg.retrieve_reffiles(update=True)

# download a particular version, but do not use it
reffile = cfg.retrieve_reffiles(version='1.0.1', update=False)

The update=True flag will use these versions for the remainder of this session. One can list available reference libraries or swap between them:

# print all config files available
cfg.help_refmanifest()

# swap the reference file versions
cfg.set_reffiles(refversion='1.0.1')

# show the manifest again, to see the new files were used
cfg.help_refmanifest()

Warning

Each time that slitlessutils is imported, it will use the most advanced version of the reference files that are cached in the user’s home directory: $HOME/.slitlessutils

3.2. Global Variables (Config())

To ensure consistency between several major subcomponents of slitlessutils, global variables are stored in the singleton configuration class. These variables are:

Table 3.1 Global Variables

Variable Name	Data Type	Purpose
fluxscale	float	The numeric scale of the spectral elements. This is important to avoid numeric underflow errors (in some cases).
fluxunits	str	The physical units of the spectral elements.
compression	str	The type of data compression used in the HDF5 files as implemented by h5py.
compression_opts	int	The compression level used in the HDF5 files as implemented by h5py.

The default values are set in the file $HOME/.slitlessutils/<VERSION_NUMBER>/defaults.json. These versions can be accessed and/or adjusted programmatically as either dictionary-like or attribute-like access and saved to a file for usage later:

# change value using dict-like access
cfg['fluxscale'] = 1.

# change value using attribute-like access
cfg.fluxunits = 'erg/s/cm**2/micron'

# save file to a local config
cfg.write("myconf.json")

Note

One can manually edit the defaults file, however new reference files packages will come with their own defaults.json file. Therefore, we recommend programmatically alter the settings to ensure consistency in results if the reference files are updated.