Python Logging - Set Date as Filename

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I am working on implementing logging within my Python project and have hit a bit of a snag. I am trying to set up my logging such that the Handlers, and Formatters are all organized into a configuration file. What I am trying to do at the moment is to set up my fileHandler such that it will create a log file that looks something like this: YYYY_MM_DD.log obviously with the Y's representing the year, M's representing the month, and D's representing the day.

This is what I have attempted with my config file:

[loggers]
keys=root,MainLogger

[handlers]
keys=fileHandler, consoleHandler

[formatters]
keys=logFormatter, consoleFormatter

[logger_root]
level=DEBUG
handlers=fileHandler

[logger_MainLogger]
level=DEBUG
handlers=fileHandler, consoleHandler
qualname=MainLogger
propagate=0

[handler_consoleHandler]
class=StreamHandler
level=DEBUG
formatter=consoleFormatter
args=(sys.stdout,)

[handler_fileHandler]
class=FileHandler
level=DEBUG
formatter=logFormatter
args=(datetime.now().strftime('%Y_%m_%d.log'), 'a')

[formatter_logFormatter]
format=%(asctime)s | %(levelname)-8s | %(lineno)04d | %(message)s

[formatter_consoleFormatter]
format=%(asctime)s | %(levelname)-8s | %(fillname)s-%(funcName)s-%(lineno)04d | %message)s

The file I am using to test the configuration is pretty simple:

import logging
import logging.config

logging.config.fileConfig('logging.conf')
logger = logging.getLogger('MainLogger')
logger.debug("TEST")

The specific error I am getting at the moment is:

configparser.InterpolationSyntaxError: '%' must be followed by '%' or '(', found: "%Y_%m_%d.log'), 'a')"

I've tried changing the %Y, %m, and %d as the error says, but that doesn't fix the problem. How do I go about setting up the config file so that my log files look the way I want them to?

I should note when I change the filename to test.log everything worked fine, so this is the only error I seem to be having with this.

logging python
11 Answers
user_12835670

Using double '%'-characters in the format string in combination with the approach suggested by Abhishek led to a working solution in my case (Python 3.5):

The filehandler in the config file should then look similar to this one:

[handler_fileHandler]
class=FileHandler
level=DEBUG
formatter=defaultFormatter
args=(__import__("datetime").datetime.now().strftime('/your_path/your_file_name_%%Y-%%m-%%d_%%H-%%M-%%S.log'), 'a')
user_100260700

This post is old, but for anyone still struggling with any such issue of dynamic naming of filenames from logging.conf while calling logging.config.fileConfig() you can pass the variables and use them in the logging configuration file. Eg:

logging.conf

args=('my_log_%(date)s.log','w')

python.py

import logging.config
logging.config.fileConfig('logging.conf', defaults={'date':datetime.now()})

You might wanna format the date while using it here.

In the same fashion, any number of variables could be used.

user_107049520

I wanted to keep all of my logging configurable through the config file and wasn't satisfied with the answers here manually adding the handler through the code. The solution I came up with is to create a handler class inheriting FileHandler which appends the date to the filename parameter before calling the FileHandler constructor:

import os
from logging import FileHandler
from datetime import datetime

class TimestampedFileHandler(FileHandler):
    def __init__(self, filename, mode='a', encoding=None, delay=False):
        filename, extension = os.path.splitext(filename)
        filename = f"{filename}_{datetime.now().strftime('%Y-%m-%d_%H-%M-%S')}{extension}"
        FileHandler.__init__(self, filename, mode, encoding, delay)

You can then use the TimestampedFileHandler in your config file and set its level, formatter, and parameters together with the other handlers.

user_154798240

This also works

from datetime import datetime
log_file = str(datetime.utcnow().strftime('%m_%d_%Y_%I_%M_%S')) + '.log'
logging.basicConfig(filename=log_file, format='%(levelname)s | %(asctime)s | %(message)s', datefmt='%m/%d/%Y %I:%M:%S %p', level=logging.DEBUG)

Logfile name:04_30_2018_10_03_01.log

user_5950900

My solution for my python product is to keep the configuration file with a path to a fixed log file such as:

[handler_fileHandler] <br>
class=FileHandler <br>
level=DEBUG <br>
formatter=defaultFormatter <br>
args=('../projectnamespace/data/logs/logfile.log',)

and for each day I will move the log file to older folder logs so by doing that I avoid having a huge log files for later reading....

log_path = str((Path(__file__).parent / 'data' / 'logs' / 'logfile.log').absolute())

log_file_date_created = None 
if platform.system() == 'Windows':
    log_file_date_created = datetime.fromtimestamp(os.path.getctime(log_path))
else:
    stat = os.stat(log_path)
    try:
        log_file_date_created = stat.st_birthtime
    except AttributeError:
        # running in Linux. No easy way to get creation dates here,
        # we get when its content was last modified.
        return stat.st_mtime

if log_file_date_created != None and abs(datetime.today().day - log_file_date_created.day) >= 1:
    file_date = str(log_file_date_created.strftime("%m_%d_%Y")) + '_logfile.log'
    log_path_new_name = str((Path(__file__).parent / 'data' / 'logs' / 'older' /  file_date ).absolute())
    os.replace(log_path, log_path_new_name)
user_134914040

I created class called LoggingService and use it's in other python file

import logging
from logging.handlers import RotatingFileHandler
from datetime import datetime

class LoggingService:

    def namer(name):
        now = datetime.now()
        date_time = now.strftime("%Y-%m-%d")
        return name[:-1] + date_time +"."+name[-1:]
      

    LOG_FORMAT = "%(levelname)s %(asctime)s - %(name)s - %(message)s"
    log_file = "your inital log file location"

    rotate_handler = RotatingFileHandler(
        filename=log_file,
        mode='a',
        maxBytes=256,
        backupCount=8,
        encoding=None,
        delay=False
    )

    logging.basicConfig(
        level=logging.DEBUG,
        format=LOG_FORMAT,
        datefmt='%m/%d/%Y %I:%M:%S %p',
        handlers=[rotate_handler]
    )

    rotate_handler.namer = namer

    @staticmethod
    def get_logger(name):
        return logging.getLogger(name)
user_160559930
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