Skip to content

Latest commit

 

History

History
157 lines (115 loc) · 4.32 KB

logging.md

File metadata and controls

157 lines (115 loc) · 4.32 KB
Raw

Logging module

Here we can take a look at using the logging module.

To include line numbers in your log messages, you can modify the format string in the basicConfig method of the logging module. The format string can include various attributes of the log record, such as the line number where the log call was made.

logging.basicConfig(level=logging.INFO,
                    format='%(asctime)s - %(levelname)s - %(filename)s:%(lineno)d - %(message)s')

Example usage

  • %(asctime)s will be replaced by the time of the log record creation.
  • %(levelname)s will be replaced by the level of the log record (e.g., INFO, ERROR).
  • %(filename)s will be replaced by the filename where the log call was made.
  • %(lineno)d will be replaced by the line number where the log call was made.
  • %(message)s will be replaced by the log message.

This configuration will apply to all log messages in your script and will include the line number in each log message, which is helpful for pinpointing the location of events and issues in your code.

import logging

logging.basicConfig(
    filename="app.log",
    filemode="w",
    format="%(name)s - %(levelname)s - %(messages)s"
)

logging.warning("This will get logged to the file")
  • filename="app.log": This is the file we are writing our logs too
  • filemode="w": Setting filemode to w will overwrite the default which is append, everytime the program runs we will get new log info
  • format: Gives the ability to customise the log message output with this example would be root - WARNING - This will get logged to the file

basicConfig(**kwargs) can only be called once and is to be placed before you start logging messages.

Formatting the Output

You're able to format the log output by using the different LogRecord attributes for example you can do the following:

logging.basicConfig(format="%(process)d - %(levelname)s - %(message)s"

>>> 12345 - WARNING - This is a warning msg

%(process)d: Process ID (if available).

Logging Time of log

You're able to add the time of the logged message, to give your log files more readability

logging.basicConfig(
  format="%(asctime)s - %(message)s",
  datefmt="%d-%b-%y %H:%M:%S"
)
logging.warning('Admin logged out')

>>> 07-May-21 13:23:03 - Admin logged out

Logging variable data

We're able to pass variables into our logging information, for example this could be good when a user is logged in for example

user = "Paul"
logging.error(f'{user} caused an error")

>>> Paul caused an error

Capturing Stack Traces

Here we're able to log the actual error message

import logging

a = 5
b = 0

try:
    c = a / b
except Exception as e:
    logging.error('Exception was raised', exc_info=True)

Using exc_info=True will log the error message along with what we passed. The output would be the following:

ERROR:root:Exception was raised
Traceback (most recent call last):
  File "/Users/paul/Developer/pycharm/playground_venv/main.py", line 7, in <module>
    c = a / b
ZeroDivisionError: division by zero

This way we're able to see that the reason for the crash was an ZeroDivisionError: division by zero

Alternativly we could log logging.exception() which is the same as logging.error(exc_info=True) if you wanted to log the exception on a different rule you can do the following logging.warning(exc_info=True)

Creating a custom logger

import logging

logger = logging.getLogger(__name__)

c_handler = logging.StreamHandler()
f_handler = logging.FileHandler('file.log')

"""
only logs WARNING or above will be logged &
ERROR will be logged to file.
"""
c_handler.setLevel(logging.WARNING)
f_handler.setLevel(logging.ERROR)

""" this will provide the same info but the file will have a timestamp """
c_format = logging.Formatter('%(name)s - %(levelname)s - %(message)s')
f_format = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')

""" assigns the formatters to the handlers """
c_handler.setFormatter(c_format)
f_handler.setFormatter(f_format)

logger.addHandler(c_handler)
logger.addHandler(f_handler)

""" test the custom logger """
logger.warning('This is an WARNING')
logger.error('This is an ERROR')