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logging Module Complexity

The logging module provides functionality for flexible event logging, with different severity levels and output destinations.

Complexity Reference

Operation Time Space Notes
logging.basicConfig() O(1) O(1) Configure logging
logger.debug/info/warning/error() O(k) O(1) k = message length
getLogger() O(1) avg O(1) Get logger instance
Formatting message O(k) O(k) k = formatted string

Basic Usage

Simple Logging

import logging

# Configure logging - O(1)
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(levelname)s - %(message)s'
)

# Log messages - O(k)
logging.debug('Debug message')      # Not shown (level=INFO)
logging.info('Info message')        # O(10)
logging.warning('Warning message')  # O(15)
logging.error('Error message')      # O(13)

Logger Instances

import logging

# Get logger - O(1)
logger = logging.getLogger(__name__)

# Set level - O(1)
logger.setLevel(logging.DEBUG)

# Log messages - O(k)
logger.debug('Debug: %s', variable)      # O(k)
logger.info('Processing: %s', item)      # O(k)
logger.warning('Issue: %s', issue)       # O(k)
logger.error('Error: %s', error)         # O(k)

Configuration

Handlers and Formatters

import logging

# Create logger - O(1)
logger = logging.getLogger('myapp')
logger.setLevel(logging.DEBUG)

# File handler - O(1)
file_handler = logging.FileHandler('app.log')
file_handler.setLevel(logging.ERROR)

# Console handler - O(1)
console_handler = logging.StreamHandler()
console_handler.setLevel(logging.INFO)

# Formatter - O(1)
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
file_handler.setFormatter(formatter)
console_handler.setFormatter(formatter)

# Add handlers - O(1) each
logger.addHandler(file_handler)      # O(1)
logger.addHandler(console_handler)   # O(1)

# Log - O(k)
logger.info('Application started')   # O(k)

Log Levels

Severity Levels

import logging

# Levels (in order) - O(1) check
logging.DEBUG       # 10 - Detailed info for debugging
logging.INFO        # 20 - Confirmation events
logging.WARNING     # 30 - Something unexpected
logging.ERROR       # 40 - Serious problem
logging.CRITICAL    # 50 - Very serious problem

# Set level - O(1)
logger.setLevel(logging.WARNING)

# Only WARNING and above are logged
logger.debug('Not logged')      # Skipped
logger.warning('Is logged')     # O(k)

Common Patterns

Application Logging

import logging

# Setup - O(1)
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s',
    filename='app.log'
)

logger = logging.getLogger(__name__)

def process_file(filename):
    try:
        logger.info(f'Processing {filename}')      # O(k)
        with open(filename) as f:
            data = f.read()  # O(n)
        logger.debug(f'Read {len(data)} bytes')    # O(k)
        return process(data)
    except FileNotFoundError:
        logger.error(f'File not found: {filename}')  # O(k)
        return None
    except Exception as e:
        logger.exception(f'Unexpected error: {e}')   # O(k)
        return None

Exception Logging

import logging

logger = logging.getLogger(__name__)

try:
    result = risky_operation()  # Might fail
except ValueError as e:
    logger.error(f'Invalid value: {e}')     # O(k)
except Exception as e:
    logger.exception('Unexpected error')    # O(k) - includes traceback

Performance Considerations

Message Formatting

import logging

logger = logging.getLogger(__name__)

# Lazy formatting - O(1) if not logged
logger.debug('User %s logged in', username)  # Only format if DEBUG level

# vs eager formatting - O(k) always
logger.debug(f'User {username} logged in')   # Always format string

# Lazy approach is more efficient when DEBUG is disabled

File I/O

import logging

# File handler - O(k) to write
handler = logging.FileHandler('app.log')

# Buffering affects performance
# Default: buffered (fast)
# Unbuffered: flush each write (slow but safer)

# Rotating file handler - O(k) per write
rotating = logging.handlers.RotatingFileHandler(
    'app.log',
    maxBytes=1000000,  # 1MB
    backupCount=5      # Keep 5 backups
)

Version Notes

  • Python 2.x: logging module available
  • Python 3.x: Enhanced with better formatting
  • All versions: O(k) logging complexity

Best Practices

✅ Do:

  • Use logging instead of print() for production
  • Set appropriate log levels
  • Use lazy formatting with %s
  • Include context in messages
  • Use exception() for exceptions

❌ Avoid:

  • Logging sensitive information (passwords)
  • Excessive debug logging in production
  • Eager string formatting
  • Using print() in libraries