Defaults for images and headers
error_level is the problem level (see BatteryRunners) at which an error will be
raised, by the batteryrunners
log_raise method. Thus a level of 0 will
result in an error for any problem at all, and a level of 50 will mean no errors
will be raised (unless someone’s put some strange problem_level > 50 code in).
logger is the default logger (python log instance)
To set the log level (log message appears for problem of level >= log level),
logger.level = 40.
As for most loggers, if
logger.level == 0 then a default log level is used -
logger.getEffectiveLevel() to see what that default is.
logger.level = 1 to see all messages.
Context manager to set log error level
Context manager to prevent global logger from printing