I've believe that print is more functional that log for debugging purpose, because it's true that logging is better for "offline" debug (and issue-sharing) but, it's more difficult for error at "runtime" because with print I've exactly the timing of issues, and so I can discover the synchrony between elements more easily, specially for error that lock the regular execution of a program (which in most of case impeding the logging...). However, after debugging phase, I'm going to remove this print or replace them with a log.debug (but only if they are really necessary or useful).
Thanks to you for attention ;)