fail w/o strandseq

[ptrebert]

the pipeline must immediately fail if not strand-seq data have been found (the glob wildcard expansion in the beginning).

[mir-cat]

Is there a particular exception to raise or is ValueError acceptable?

[ptrebert]

as long as you raise an informative error message, a generic ValueError is certainly fine (just for the sake of completeness: there is also a FileNotFound exception).