Specifying a custom logging Linux filepath in Python 2

Question

I'm trying to understand how logfiles work with the Python 2 logging module.

I know that I can save the log output to a text file using something like:

logging.basicConfig(filename='example.log',level=logging.DEBUG)

It's not clear to me from the documentation on:

Whether or not absolute filename paths are valid
The proper syntax for specifying relative paths (assuming that ../example.log is valid).

If I execute this script from /home/bob, how do I specify that I want the logfile saved to the /tmp directory instead - using both absolute and relative paths?

Is logging.basicConfig(filename='../../tmp/example.log') valid?

Similarly, is logging.basicConfig(filename='/tmp/example.log') valid?

Chen A. · Accepted Answer · 2017-08-31 14:23:59Z

2

When stating just the filename, it would be written to the current directory. Using Python IDLE you can check that as follows

>>> import logging
>>> logging.basicConfig(filename='relative.log')
>>> logging.info('test')

C:\Python27\relative.log

My working dir is Python27, and I have a file there named relative.log with my logged message.

When you change the file location to ../relative.log, I get a new file at the parent directory of Python27. So relative path does work for logging:

>>> import logging
>>> logging.basicConfig(filename='../relative.log')
>>> logging.info('test123')

C:\relative.log

And logging module also supports absolute path:

>>> logging.basicConfig(filename=r'c:\abs_path.log')
>>> logging.info('test')

C:\abs_path.log

It is always better to use absolute path, as explicit is better than implicit.

answered Aug 31, 2017 at 14:23

Chen A.

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2 Comments

alex Over a year ago

Thanks - this is admittedly sort of a dumb question. I've verified that absolute paths will also work with Linux environments.

Chen A. Over a year ago

It will, just note if you are running it on Windows platform, you need to add r for raw before writing the path, otherwise it will throw an error unless you escape every slash in your path

Tristan · Accepted Answer · 2017-08-31 14:30:31Z

1

They are both valid. But relative paths (with ..) will select different files depending on the directory you are in when you run it.

So when you run logger.py in /home/user/projects/python and the filename is ../log.txt the file will be saved in /home/user/projects. On the other hand when you run the script in /home/user then log.txt will be saved in /home/.

Absolute paths always work and are more reliable. If you want a file in the current directory I recommend this approach:

basedir = os.path.abspath(os.path.dirname(__file__))
filename = os.path.join(basedir, 'file.txt')

answered Aug 31, 2017 at 14:30

Tristan

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