This does not seem to accomplish anything besides hiding the "using the slow, pure python stringprep" warning, unless you import logging and add another handler before to the "slixmpp" logger BEFORE importing slixmpp.
import logging
logging.getLogger("slixmpp").addHandler(logging.StreamHandler())
from slixmpp import ...I may have failed to understand if this accomplishes something else, but I think this was a workaround to get rid of warning in some old python versions that aren't supported now anyway.
Hiding the stringprep warning by default defeats the point of having a warning in the first place IMHO.