'Convenience method to configure a stream logger.
:type logger_name: str
:param logger_name: The name of the logger to configure
:type log_level: str
:param log_level: The log level to set for the logger.  This
is any param supported by the ``.setLevel()`` method of
a ``Log`` object.
:type stream: file
:param stream: A file like object to log to.  If none is provided
then sys.stderr will be used.
:type format_string: str
:param format_string: The format string to use for the log
formatter.  If none is provided this will default to
``self.LOG_FORMAT``.'

def set_stream_logger(self, logger_name, log_level, stream=None, format_string=None):

    log = logging.getLogger(logger_name)
    log.setLevel(logging.DEBUG)
    ch = logging.StreamHandler(stream)
    ch.setLevel(log_level)
    if (format_string is None):
        format_string = self.LOG_FORMAT
    formatter = logging.Formatter(format_string)
    ch.setFormatter(formatter)
    log.addHandler(ch)
