About NOTSET in python logging

Question

As the logger.setLevel doc says: When a logger is created, the level is set to NOTSET (which causes all messages to be processed when the logger is the root logger, or delegation to the parent when the logger is a non-root logger). Note that the root logger is created with level WARNING. so I think if I create a root logger, with level NOTSET, the debug and info log will display. The code use basicConfig to set root logger's level to NOTSET is right: ``` #!/usr/bin/env python # -*- coding: utf-8 -*- import logging logging.basicConfig(level=logging.NOTSET) log = logging.getLogger() log.debug('debug') log.info('info') log.warning('warning') log.error('error') log.critical('critical') ``` and output is: ``` DEBUG:root:debug INFO:root:info WARNING:root:warning ERROR:root:error CRITICAL:root:critical ``` But if I create a root logger, and add handler with NOTSET level to it, such as: ``` #!/usr/bin/env python # -*- coding: utf-8 -*- import logging log = logging.getLogger() hd = logging.Str…

Accepted Answer

OK, I misunderstand the `Logger's level` and `Handler's Level`, in the doc:

The setLevel() method, just as in logger objects, specifies the lowest severity that will be dispatched to the appropriate destination. Why are there two setLevel() methods? The level set in the logger determines which severity of messages it will pass to its handlers. The level set in each handler determines which messages that handler will send on.

If I change code to this, will be ok:

```
#!/usr/bin/env python
# -*- coding: utf-8 -*-

import logging

log = logging.getLogger()
log.setLevel(logging.NOTSET) # Set Logger's level to NOTSET, default is WARNING
#print "Logger's Level: ", log.level
hd = logging.StreamHandler()
hd.setLevel(logging.NOTSET)
#print "Handler's Level: ", hd.level
log.addHandler(hd)

log.debug('debug')
log.info('info')
log.warning('warning')
log.error('error')
log.critical('critical')
```

About NOTSET in python logging

Solution

Problem