Code for Logging in Python Tutorial

logger_simple.py

import logging

# make a debug message
logging.debug("This is a simple debug log")

# make an info message
logging.info("This is a simple info log")

# make a warning message
logging.warning("This is a simple warning log")

# make an error message
logging.error("This is a simple error log")

# make a critical message
logging.critical("This is a simple critical log")

# just mapping logging level integers into strings for convenience
logging_levels = {
    logging.DEBUG: "DEBUG", # 10
    logging.INFO: "INFO", # 20
    logging.WARNING: "WARNING", # 30
    logging.ERROR: "ERROR", # 40
    logging.CRITICAL: "CRITICAL", # 50
}

# get the current logging level
print("Current logging level:", logging_levels.get(logging.root.level))

# get the current logging format
print("Current logging format:", logging.BASIC_FORMAT)

logger_basic.py

import logging

# make a basic logging configuration
# here we set the level of logging to DEBUG
logging.basicConfig(
    level=logging.DEBUG
)

# make a debug message
logging.debug("This is a simple debug log")

# make an info message
logging.info("This is a simple info log")

# make a warning message
logging.warning("This is a simple warning log")

# make an error message
logging.error("This is a simple error log")

# make a critical message
logging.critical("This is a simple critical log") 

logger_config.py

import logging

logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s - %(levelname)s - %(message)s",
)

logging.info("This is an info message!")

logger_datefmt.py

import logging

logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s - %(levelname)s - %(message)s",
    datefmt="[%Y-%m-%d] %H:%M:%S",
)

logging.info("This is an info message!")

logger_file.py

import logging
import math

logging.basicConfig(level=logging.DEBUG,
                    handlers=[logging.FileHandler('logs.log', 'a', 'utf-8')],
                    format="%(asctime)s %(levelname)-6s - %(funcName)-8s - %(filename)s - %(lineno)-3d - %(message)s",
                    datefmt="[%Y-%m-%d] %H:%M:%S - ",
                    )

logging.info("This is an info log")

def square_root(x):
    logging.debug(f"Getting the square root of {x}") 
    try:
        result = math.sqrt(x)
    except ValueError:
        logging.exception("Cannot get square root of a negative number")
        # or
        # logging.error("Cannot get square root of a negative number", exc_info=True)
        return None
    logging.info(f"The square root of {x} is {result:.5f}")
    return result

square_root(5)
square_root(-5)

logger_handlers.py

import logging

# return a logger with the specified name & creating it if necessary
logger = logging.getLogger(__name__)

# create a logger handler, in this case: file handler
file_handler = logging.FileHandler("file.log")
# set the level of logging to INFO
file_handler.setLevel(logging.INFO)

# create a logger formatter
logging_format = logging.Formatter("%(asctime)s - %(levelname)s - %(message)s")

# add the format to the logger handler
file_handler.setFormatter(logging_format)

# add the handler to the logger
logger.addHandler(file_handler)

# use the logger as previously
logger.critical("This is a critical message!")