storing logger messages in a string

Question

I wanted to store all the intermediate log messages (warn, info, error) to a string in python and finally at the end of program, display everything as a report to the consol

Answer 1

It can be as simple as logging to a StringIO object:

import logging
try:
    from cStringIO import StringIO      # Python 2
except ImportError:
    from io import StringIO

log_stream = StringIO()    
logging.basicConfig(stream=log_stream, level=logging.INFO)

logging.info('hello world')
logging.warning('be careful!')
logging.debug("you won't see this")
logging.error('you will see this')
logging.critical('critical is logged too!')

print(log_stream.getvalue())

Output

INFO:root:hello world
WARNING:root:be careful!
ERROR:root:you will see this
CRITICAL:root:critical is logged too!

---

If you want to log only those messages at levels WARN, INFO and ERROR you can do it with a filter. LevelFilter below checks each log record's level no, allowing only those records of the desired level(s):

import logging
try:
    from cStringIO import StringIO      # Python 2
except ImportError:
    from io import StringIO

class LevelFilter(logging.Filter):
    def __init__(self, levels):
        self.levels = levels

    def filter(self, record):
        return record.levelno in self.levels

log_stream = StringIO()    
logging.basicConfig(stream=log_stream, level=logging.NOTSET)
logging.getLogger().addFilter(LevelFilter((logging.INFO, logging.WARNING, logging.ERROR)))

logging.info('hello world')
logging.warning('be careful!')
logging.debug("you won't see this")
logging.error('you will see this')
logging.critical('critical is no longer logged!')

print(log_stream.getvalue())

Output

INFO:root:hello world
WARNING:root:be careful!
ERROR:root:you will see this