A global logger is used throughout the library. You may configure it or even replace it with your own. Customizing the default log should be sufficient for most purposes though.
The default logger is available as cssutils.log. It has the following methods which are basically the same as defined for standard logging loggers:
log.setLevel(level) and log.getEffectiveLevel(), example:
import logging
cssutils.log.setLevel(logging.FATAL)
log.addHandler(h) and log.removeHandler(h)
log.*(msg) where * is one of debug, info, warn, error or fatal/critical
Additional method: cssutils.log.setLog(newlog): To replace the default log which sends output to stderr.
See also cssutils.css.Property.validate() for details on how properties log.