How to do a partial expand in Snakemake?

Question

I\'m trying to first generate 4 files, for the LETTERS x NUMS combinations, then summarize over the NUMS to obtain one file per element in LETTERS:

LETTERS =         


        

Answer 1

Indeed, braces need to be escaped when you want to ignore them in expand. It relies on str.format, and hence any rules from format apply to expand as well.