10000 [3.11] Provided better example for logging cookbook (GH-101164) (GH-101184) by miss-islington · Pull Request #101184 · python/cpython · GitHub
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[3.11] Provided better example for logging cookbook (GH-101164) (GH-101184) #101184

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Jan 20, 2023
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[3.11] Provided better example for logging cookbook (GH-101164) (GH-101184) #101184

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41 changes: 31 additions & 10 deletions Doc/howto/logging-cookbook.rst
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Expand Up @@ -1982,26 +1982,47 @@ Using a rotator and namer to customize log rotation processing
--------------------------------------------------------------

An example of how you can define a namer and rotator is given in the following
snippet, which shows zlib-based compression of the log file::
runnable script, which shows gzip compression of the log file::

import gzip
import logging
import logging.handlers
import os
import shutil

def namer(name):
return name + ".gz"

def rotator(source, dest):
with open(source, "rb") as sf:
data = sf.read()
compressed = zlib.compress(data, 9)
with open(dest, "wb") as df:
df.write(compressed)
with open(source, 'rb') as f_in:
with gzip.open(dest, 'wb') as f_out:
shutil.copyfileobj(f_in, f_out)
os.remove(source)

rh = logging.handlers.RotatingFileHandler(...)

rh = logging.handlers.RotatingFileHandler('rotated.log', maxBytes=128, backupCount=5)
rh.rotator = rotator
rh.namer = namer

These are not "true" .gz files, as they are bare compressed data, with no
"container" such as you’d find in an actual gzip file. This snippet is just
for illustration purposes.
root = logging.getLogger()
root.setLevel(logging.INFO)
root.addHandler(rh)
f = logging.Formatter('%(asctime)s %(message)s')
rh.setFormatter(f)
for i in range(1000):
root.info(f'Message no. {i + 1}')

After running this, you will see six new files, five of which are compressed:

.. code-block:: shell-session

$ ls rotated.log*
rotated.log rotated.log.2.gz rotated.log.4.gz
rotated.log.1.gz rotated.log.3.gz rotated.log.5.gz
$ zcat rotated.log.1.gz
2023-01-20 02:28:17,767 Message no. 996
2023-01-20 02:28:17,767 Message no. 997
2023-01-20 02:28:17,767 Message no. 998

A more elaborate multiprocessing example
----------------------------------------
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