I think I get it: Python sets custom delimiters that include '-' because for the Python REPL, it’s not possible to have one identifier with a dash, so it’s considered a delimiter and when you press tab, a new completion is started.  For a custom REPL however, you may want to have dashes as legal parts of your completed words, so you want to call set_completer_delims.  Reclassifying as a doc patch.