I once wrote a custom report generator that could pair basically arbitrary input formats (pluggable, I think by the time I was done I'd written importers for CSV, fixed width, and JSON data) and output custom PDF output, with fully-user definable formatting/elements - using XML "templates" just because I didn't want to write a custom parser. Included loops, if statements, etc, and some pretty fancy output features (e.g. output N records per page, with custom sorting, headers/footers/etc). Used ReportLab for the PDF generation. Whole thing was under 1k lines of Python 2.