Logging in server code

[ppigazzini]

When running a python program with systemd both stdout and stderr are fully buffered, so there is a delay (sometimes big) to view the entries in the journal.

• test program:

# test_print.py
import time
import sys
for i in range(10)
    print(i, file=sys.stderr)
    time.sleep(1)

• systemd unit:

# /ets/systemd/system/test_print.service
[Unit]
Description=test print() to journal
After=network.target

[Service]
Type=simple
ExecStart=/home/usr00/env/bin/python3 /home/usr00/test_print.py
User=usr00
WorkingDirectory=/home/usr00

[Install]
WantedBy=multi-user.target

• commands:

sudo systemctl daemon-reload
sudo systemctl start test_print
# check in another terminal
sudo journalctl -f -u test_print

Here some information:

• stdout buffering types: https://realpython.com/python-print/#buffering-print-calls https://eklitzke.org/stdout-buffering

• ways to get unbuffered python prints: https://stackoverflow.com/questions/230751/how-can-i-flush-the-output-of-the-print-function-unbuffer-python-output For development/debug the simple ways are:

  • use the switch python3 -u during development/debug, eg python3 -u pserve development.ini
  • redefine the print() with the partial function in each server module: print = partial(print, flush=True)

• Pyramid and python logging system: https://docs.pylonsproject.org/projects/pyramid/en/latest/narr/logging.html https://docs.python.org/3/library/logging.html https://docs.python.org/3/howto/logging.html Pyramid creates the configuration to use the standard logging python library, see the fishtest code: https://github.com/glinscott/fishtest/blob/2e0b9838d3f7b615a70c5fc2857341038e7213af/server/production.ini#L35-L65