17

Currently, this is what I have (testlog.py):

import logging
import logging.handlers

filename = "example.log"

logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")

handler = logging.handlers.RotatingFileHandler(filename, mode = 'w', backupCount = 5)
handler.setLevel(logging.DEBUG)
handler.setFormatter(formatter)
logger.addHandler(handler)

ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG)
ch.setFormatter(formatter)
logger.addHandler(ch)

for i in range(10):
   logger.debug("testx") #where I alternate x from 1 thru 9 to see output

It currently successfully prints out to the console and to example.log, which is what I want.

Every time I run it, it makes a new file and replaces the old example.log like so:

  • run with logger.debug("test1") - example.log will contain test1 10 times like it should.

  • run with logger.debug("test2") - it rewrites example.log to contain test2 10 times.

  • etc...

However, I would like for the code to make a new log file every time I run the program so that I have:

example.log
example.log1
example.log2 
...
example.log5

In conclusion, I'd like for this file to print the log message to the console, to the log file, and I would like a new log file (up to *.5) whenever I run the program.

Tomerikoo
  • 18,379
  • 16
  • 47
  • 61
practicemakesperfect
  • 367
  • 2
  • 4
  • 9
  • 1
    SOLVED! all I did was add `logging.handlers.RotatingFileHandler.doRollover(handler)` at the end – practicemakesperfect Jun 19 '17 at 17:18
  • 1
    Don't do it at the end - if your script fails mid-point end doesn't reach the end you won't be getting the new log file on the next start. Do it when initializing your logging. – zwer Jun 19 '17 at 17:21

2 Answers2

39

logging.handlers.RotatingFileHandler rotates your logs based either on size or on date, but you can force it to rotate using RotatingFileHandler.doRollover() so something like:

import logging.handlers
import os

filename = "example.log"

# your logging setup

should_roll_over = os.path.isfile(filename)
handler = logging.handlers.RotatingFileHandler(filename, mode='w', backupCount=5)
if should_roll_over:  # log already exists, roll over!
    handler.doRollover()

# the rest of your setup...

Should work like a charm.

zwer
  • 24,943
  • 3
  • 48
  • 66
  • 2
    it creates empty log files on each run – ybonda Sep 21 '20 at 15:38
  • 1
    set `delay` = True, it avoids creation of empty log files – Dman Cannon Jan 08 '21 at 06:15
  • 2
    How do I add a timestamp instead of .log.1, .log.2 ? – Vrishank Jun 28 '21 at 06:50
  • 3
    @Vrishank `RotatingFileHandler` uses the base filename to determine the rotated log name, you cannot set it to use timestamps or anything else except the `.` for its rotated files. That being said, this being Python, you can always override the internals to have it do your bidding, you can check out one way to do it in [this answer](https://stackoverflow.com/a/39351132/7553525). – zwer Jun 28 '21 at 11:47
  • 1
    @ybonda, it works for me if I remove mode = 'w' from RotatingFileHandler – Andrei May 17 '22 at 17:23
0

If you change the mode to 'a' in the solution posted by zwer, then you get a single empty log file at the first run, after that it will work as intended. Just increase the backupCount by +1 :-)

anom
  • 11