12 - Real Development Modules

📌 What You'll Learn

• •os module - Operating system interface
• •sys module - System-specific parameters
• •logging module - Application logging
• •argparse module - Command-line arguments
• •pathlib module - Modern path handling

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📁 os Module

The os module provides a way to interact with the operating system.

Directory Operations

import os

# Current working directory
cwd = os.getcwd()
print(f"Current directory: {cwd}")

# Change directory
os.chdir('/tmp')

# List directory contents
files = os.listdir('.')  # Current directory
files = os.listdir('/home')  # Specific path

# Create directory
os.mkdir('new_folder')  # Single directory
os.makedirs('path/to/nested/folder', exist_ok=True)  # Nested

# Remove directory
os.rmdir('empty_folder')
os.removedirs('path/to/nested/folder')  # Remove nested empty dirs

# Check if path exists
os.path.exists('/path/to/file')
os.path.isfile('/path/to/file')
os.path.isdir('/path/to/folder')

File Operations

import os

# Rename file/directory
os.rename('old_name.txt', 'new_name.txt')

# Remove file
os.remove('file_to_delete.txt')

# Get file info
info = os.stat('file.txt')
print(f"Size: {info.st_size} bytes")
print(f"Modified: {info.st_mtime}")

# Walk through directory tree
for root, dirs, files in os.walk('/path'):
    print(f"Directory: {root}")
    for file in files:
        print(f"  File: {file}")

Path Operations

import os.path

# Join paths (cross-platform)
path = os.path.join('folder', 'subfolder', 'file.txt')

# Split path components
dirname = os.path.dirname('/path/to/file.txt')  # '/path/to'
basename = os.path.basename('/path/to/file.txt')  # 'file.txt'
name, ext = os.path.splitext('file.txt')  # ('file', '.txt')

# Absolute path
abs_path = os.path.abspath('relative/path')

# Expand user (~)
home = os.path.expanduser('~')

Environment Variables

import os

# Get environment variable
home = os.environ.get('HOME')
path = os.environ.get('PATH', 'default_value')

# Set environment variable
os.environ['MY_VAR'] = 'value'

# Get all environment variables
for key, value in os.environ.items():
    print(f"{key}={value}")

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⚙️ sys Module

The sys module provides access to Python interpreter variables and functions.

import sys

# Command-line arguments
print(sys.argv)  # List of arguments
script_name = sys.argv[0]
if len(sys.argv) > 1:
    first_arg = sys.argv[1]

# Python version
print(sys.version)
print(sys.version_info)

# Platform
print(sys.platform)  # 'linux', 'darwin', 'win32'

# Python path
print(sys.path)  # Module search paths
sys.path.append('/custom/path')

# Exit program
sys.exit(0)  # Exit with status code

# Standard streams
sys.stdout.write("Hello\n")
sys.stderr.write("Error\n")

# Object size
size = sys.getsizeof([1, 2, 3])
print(f"List size: {size} bytes")

# Recursion limit
print(sys.getrecursionlimit())
sys.setrecursionlimit(2000)

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📝 logging Module

Professional way to track events in your application.

Basic Logging

import logging

# Basic configuration
logging.basicConfig(level=logging.DEBUG)

# Log messages at different levels
logging.debug("Debug message")     # Detailed info for debugging
logging.info("Info message")       # Confirmation that things work
logging.warning("Warning message") # Something unexpected
logging.error("Error message")     # More serious problem
logging.critical("Critical!")      # Very serious error

Logging Configuration

import logging

# Configure logging format
logging.basicConfig(
    level=logging.DEBUG,
    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s',
    datefmt='%Y-%m-%d %H:%M:%S'
)

# Log to file
logging.basicConfig(
    filename='app.log',
    level=logging.INFO,
    format='%(asctime)s - %(levelname)s - %(message)s'
)

Using Logger Objects

import logging

# Create logger
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)

# Create handlers
console_handler = logging.StreamHandler()
file_handler = logging.FileHandler('app.log')

# Set levels for handlers
console_handler.setLevel(logging.WARNING)
file_handler.setLevel(logging.DEBUG)

# Create formatters
formatter = logging.Formatter('%(name)s - %(levelname)s - %(message)s')
console_handler.setFormatter(formatter)
file_handler.setFormatter(formatter)

# Add handlers to logger
logger.addHandler(console_handler)
logger.addHandler(file_handler)

# Use logger
logger.debug("Debug message")
logger.info("Info message")
logger.warning("Warning message")

Logging Exceptions

import logging

logger = logging.getLogger(__name__)

try:
    result = 10 / 0
except ZeroDivisionError:
    logger.exception("An error occurred")  # Includes traceback

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🖥️ argparse Module

Parse command-line arguments professionally.

Basic Usage

import argparse

# Create parser
parser = argparse.ArgumentParser(description='My awesome program')

# Add arguments
parser.add_argument('filename', help='Input file name')
parser.add_argument('-o', '--output', help='Output file name')
parser.add_argument('-v', '--verbose', action='store_true', help='Verbose output')
parser.add_argument('-n', '--number', type=int, default=10, help='Number of items')

# Parse arguments
args = parser.parse_args()

# Use arguments
print(f"Input: {args.filename}")
print(f"Output: {args.output}")
print(f"Verbose: {args.verbose}")
print(f"Number: {args.number}")

Argument Types

import argparse

parser = argparse.ArgumentParser()

# Positional arguments (required)
parser.add_argument('name', help='Your name')

# Optional arguments
parser.add_argument('-a', '--age', type=int, help='Your age')

# Boolean flags
parser.add_argument('-v', '--verbose', action='store_true')
parser.add_argument('--no-cache', action='store_false', dest='cache')

# Choices
parser.add_argument('--color', choices=['red', 'green', 'blue'])

# Multiple values
parser.add_argument('--files', nargs='+', help='Input files')
parser.add_argument('--coords', nargs=2, type=float, help='X Y coordinates')

# Required optional argument
parser.add_argument('--config', required=True)

# Default values
parser.add_argument('--port', type=int, default=8080)

args = parser.parse_args()

Subcommands

import argparse

parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(dest='command')

# 'init' subcommand
init_parser = subparsers.add_parser('init', help='Initialize project')
init_parser.add_argument('--template', default='basic')

# 'build' subcommand
build_parser = subparsers.add_parser('build', help='Build project')
build_parser.add_argument('--output', '-o')

# 'run' subcommand
run_parser = subparsers.add_parser('run', help='Run project')
run_parser.add_argument('--port', type=int, default=8000)

args = parser.parse_args()

if args.command == 'init':
    print(f"Initializing with template: {args.template}")
elif args.command == 'build':
    print(f"Building to: {args.output}")
elif args.command == 'run':
    print(f"Running on port: {args.port}")

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📂 pathlib Module (Modern Path Handling)

pathlib provides an object-oriented way to handle filesystem paths.

from pathlib import Path

# Create path objects
path = Path('/home/user/documents')
current = Path.cwd()
home = Path.home()

# Path operations
new_path = path / 'subfolder' / 'file.txt'

# Path components
print(path.name)      # 'documents'
print(path.parent)    # '/home/user'
print(path.suffix)    # '.txt' for a file
print(path.stem)      # filename without extension

# Check path properties
path.exists()
path.is_file()
path.is_dir()
path.is_absolute()

# Create directories
Path('new/nested/dir').mkdir(parents=True, exist_ok=True)

# Read/write files
content = Path('file.txt').read_text()
Path('output.txt').write_text('Hello, World!')

# Iterate directory
for file in Path('.').iterdir():
    print(file)

# Glob patterns
for py_file in Path('.').glob('*.py'):
    print(py_file)

for py_file in Path('.').rglob('*.py'):  # Recursive
    print(py_file)

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📋 Summary

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🎯 Next Steps

After mastering real development modules, proceed to 13_regex to learn about pattern matching with regular expressions!