Python logging

10 Oct 2017

Pythong logging module

Loggers expose the interface that application code directly uses.
Handlers send the log records (created by loggers) to the appropriate destination.
Filters provide a finer grained facility for determining which log records to output.
Formatters specify the layout of log records in the final output.
` LogRecord`

syslog

Rsyslog

Python Logging

import logging

logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)

# create a file handler
handler = logging.FileHandler('hello.log')
handler.setLevel(logging.INFO)

# create a logging format
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
handler.setFormatter(formatter)

# add the handlers to the logger
logger.addHandler(handler)

logger.info('Hello baby')

Logger

logger names track the package/module hierarchy, and it’s intuitively obvious where events are logged just from the logger name.

Logger.setLevel() specifies the lowest-severity log message a logger will handle, where debug is the lowest built-in severity level and critical is the highest built-in severity. For example, if the severity level is INFO, the logger will handle only INFO, WARNING, ERROR, and CRITICAL messages and will ignore DEBUG messages.
Logger.addHandler() and Logger.removeHandler() add and remove handler objects from the logger object. Handlers are covered in more detail in Handlers.
Logger.addFilter() and Logger.removeFilter() add and remove filter objects from the logger object. Filters are covered in more detail in Filter Objects.

Config

logging.ini

three ways:

Creating loggers, handlers, and formatters explicitly using Python code that calls the configuration methods listed above.
Creating a logging config file and reading it using the fileConfig() function.
```
  logging.config.fileConfig('logging.conf')
```
Creating a dictionary of configuration information and passing it to the dictConfig() function.

Use rotating file handler

Level/ Severity

debug(), info(), warning(), error() and critical().

Handler

class Handler()
class logging.StreamHandler(stream=None)
class logging.NullHandler
class logging.FileHandler(filename, mode='a', encoding=None, delay=False)
class logging.handlers.WatchedFileHandler(filename[, mode[, encoding[, delay]]])
class logging.handlers.RotatingFileHandler(filename, mode='a', maxBytes=0, backupCount=0, encoding=None, delay=0)
- doRollover()
class logging.handlers.TimedRotatingFileHandler(filename, when='h', interval=1, backupCount=0, encoding=None, delay=False, utc=False)
class logging.handlers.SocketHandler(host, port)
class logging.handlers.DatagramHandler(host, port)
class logging.handlers.SysLogHandler(address=('localhost', SYSLOG_UDP_PORT), facility=LOG_USER, socktype=socket.SOCK_DGRAM)
class logging.handlers.NTEventLogHandler(appname, dllname=None, logtype='Application')
class logging.handlers.SMTPHandler(mailhost, fromaddr, toaddrs, subject, credentials=None, secure=None)
class logging.handlers.BufferingHandler(capacity)
class logging.handlers.MemoryHandler(capacity, flushLevel=ERROR, target=None)
class logging.handlers.HTTPHandler(host, url, method='GET')

misc

Logging variable data:

  logging.warning('%s before you %s', 'Look', 'leap!')

  str.format() 
  string.Template
  from string import Template
  s = Template('$who likes $what')
  s.substitute(who='tim', what='kung pao')

TODO

what is python module and __name__ variable? if the python interpreter is running that module (the source file) as the main program, it sets the special __name__ variable to have a value “__main__”. If this file is being imported from another module, __name__ will be set to the module’s name. A module’s __name__ is set equal to ‘__main__’ when read from standard input, a script, or from an interactive prompt. A module can discover whether or not it is running in the main scope by checking its own __name__, which allows a common idiom for conditionally executing code in a module when it is run as a script or with python -m but not when it is imported:

For a package, the same effect can be achieved by including a __main__.py module, the contents of which will be executed when the module is run with -m.

Asylum