Complex logging configuration in python, using the "logging" module and yaml configuration

log-config.yaml

version: 1

formatters:
  # Note that the following formats may use the 'hostname' attribute, which is non-standard.  Be sure to use an adapter
  # or a filter to get that info into the LogRecord context or ugliness will result.  
  # See:
  #   - mem_cleaner2.HostnameLoggerAdapter
  #   - https://docs.python.org/3/howto/logging-cookbook.html#adding-contextual-information-to-your-logging-output
  #
  oneLine:
    format: "%(asctime)s %(levelname)-8s -- %(message)s -- %(module)s.%(funcName)s:%(lineno)d -- %(pathname)s"
  multiLine:
    format: "%(asctime)s -- %(levelname)s\n\n%(message)s\n\n%(hostname)s -- %(module)s.%(funcName)s:%(lineno)d -- %(pathname)s"

filters:
  smtpWorthy:
    (): __main__.SmtpWorthy         # Some magic filter w/code I write to sent "restart" messages unconditionally (by 
                                    # matching regex, I guess) and critical-failure exceptions every two hours 
                                    # (between x:00 and x:10, where x is an even number).

handlers:
  console:
    class: logging.StreamHandler
    stream: ext://sys.stdout
    level: NOTSET                   # Let logger set level
    formatter: oneLine

  file:
    class: logging.handlers.RotatingFileHandler
    filename: "Logs/mem_cleaner2.log" # Directory must exist ahead of time or logging will fail (i.e., not auto-created).
    maxBytes: 10485760              # 1048576 is a megabyte
    backupCount: 10
    level: NOTSET                   # Let logger set level
    formatter: oneLine

  smtp:
    class: logging.handlers.SMTPHandler
    mailhost: smtp.ur-company.com
    fromaddr: [email protected]
    toaddrs: 
      # - [email protected]
      # - [email protected]
      - [email protected]
    subject: "mem_cleaner2.py restarted a cube (or saw a critical error)"
    timeout: 15.0                   # In seconds, I assume
    level: NOTSET                   # Let logger set level
    formatter: multiLine
    filters: [smtpWorthy]

# Unless there are other loggers declared (probably not necessary for a script this simple), there's only the root logger.
root:
  level: DEBUG
  handlers: 
    - console
    - file
    - smtp

mem_cleaner2.py

# Excerpted from my running production code.
# Probably don't need all this garbage, but oh well.
import sys
import os
import socket
import io
import traceback
import logging, logging.config
import re

import time
from ruamel.yaml import YAML            # Not built-in

# ... blah blah blah ...

def configure():

    # Get settings
    if getattr(sys, 'frozen', False):
        # PyInstaller .exe
        application_path = os.path.dirname(sys.executable)
    elif __file__:
        # "Normal" Python script
        application_path = sys.path[0]

    # 'safe' loader as opposed to 'rt' (round-trip; but we won't be writing any YAML, so no need);
    # pure Python yaml-parsing code as opposed to whatever C/C++ parser the module finds
    yamlReader = YAML(typ='safe', pure=True) 

    print( 'Attempt logging config')
    try:
        logconfig = yamlReader.load( open( application_path + r'\log-config.yaml', 'r'))
        logging.config.dictConfig( logconfig)
    except:
        logging.exception( 'Exception configuring logging')
    logger = HostnameLoggerAdapter( logging.getLogger('__main__'), {'hostname': socket.gethostname()})
    logger.debug( 'Logging configured')
    
class SmtpWorthy(logging.Filter):
    """Decides whether a particular log record is worthy of an SMTP message."""

    def filter(self, aLogRecord):
        if re.match( 'MAI-WORKSTATION-NAME', socket.gethostname()):
            # Don't be spamming people from your dev workstation.
            retval = False
        elif aLogRecord.levelno == logging.CRITICAL:
            # Top priority
            retval = True
        elif re.search('Full cube info:', aLogRecord.message):
            # Filter this out because it produces a false match on the regex below.  
            # It's a huge blob of text that just means the cube isn't running (it might be just sleeping).
            retval = False
        else:
            retval = re.search('Restarting|Detaching', aLogRecord.message)
        return retval

class HostnameLoggerAdapter( logging.LoggerAdapter):
    """
        Looks like a logger; adds current hostname (as 'hostname') to LogRecord context info.

        NOTE: Inherited constructor seems to set 'extra' attribute, so we just need to override processing.
    """
    
    def process( self, msg, kwargs):
        """Less-destructive handling of 'extra' keyword."""
        if 'extra' in kwargs:
            kwargs['extra'].update( self.extra)
        else:
            kwargs['extra'] = self.extra
        return msg, kwargs
    

Credit to https://gist.github.com/kingspp/9451566a5555fb022215ca2b7b802f19

and https://gist.github.com/kingspp/9451566a5555fb022215ca2b7b802f19#gistcomment-3078537