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The ISG is contained in a single Python module almaqa2isg which is part of the the analysis_scripts.tar package which also contains the "analysisUtils" which you will also need since the ISG uses a few of their functions.
See the Zenodo analysisUtils page (which provides a citeable DOI: 10.5281/zenodo.7502160) and the Analysis Utilities CASA Guide for details on how to install the package.
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