Capturing Python Log Output In A Variable

While working on a Sublime Text plugin, I needed to capture logging output in a variable so I could display it easily. For once, Stack Overflow^1^^ didn't have an immediate solution. After a couple hours of hacking around, I came up with the following which I hope saves others the hassle of having to build it themselves.

import logging import io

### Create the logger logger = logging.getLogger('basic_logger') logger.setLevel(logging.DEBUG)

### Setup the console handler with a StringIO object log_capture_string = io.StringIO() ch = logging.StreamHandler(log_capture_string) ch.setLevel(logging.DEBUG)

### Optionally add a formatter formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s') ch.setFormatter(formatter)

### Add the console handler to the logger logger.addHandler(ch)

### Send log messages. logger.debug('debug message') logger.info('info message') logger.warn('warn message') logger.error('error message') logger.critical('critical message')

### Pull the contents back into a string and close the stream log_contents = log_capture_string.getvalue() log_capture_string.close()

### Output as lower case to prove it worked. print(log_contents.lower())

*Note that once you call '.close()', it's possible to run into problems if the same running process tries to call the function again.*

This approach will work with external files too. If you assign the same logger (in this case 'basic_logger') it will output properly. For example, if you have an module in an external file called 'external_logger_test.py' with the content:

import logging

def log_test():

logger = logging.getLogger('basic_logger')

logger.warning('Log note from external file')

All you have to do is import it as usual in your main file (e.g. `import external_logger_test`) and then call the function:

external_logger_test.log_test()

Of course, you have to do this before you call the `log_contents = log_capture_string.getvalue()`. That's where the log data stops flowing.

_Links and Notes_

1. Stack Overflow - Friend to developers around the world. Far and away the most useful development research site there is.