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The Standard Library: Batteries Included

Python’s fame comes from its “Batteries Included” philosophy. When you install Python, you aren’t just getting a language; you’re getting a massive library of pre-written code that handles everything from cryptographic hashing to interacting with the operating system.

1. Files & Paths: `pathlib` (The Modern Standard)

In the old days, we used os.path for file manipulation. Modern Python uses pathlib, which treats files as objects rather than strings.

from pathlib import Path

# Create a path object
p = Path("docs") / "notes.txt" # Use '/' regardless of OS!

print(f"Filename: {p.name}")
print(f"Extension: {p.suffix}")
print(f"Exists? {p.exists()}")

# Read/Write without open/close
if p.exists():
    content = p.read_text()

2. Operating System & System: `os` and `sys`

os: Low-level operating system tasks (environment variables, process IDs).
sys: Interaction with the Python interpreter itself.

import os
import sys

# Get an environment variable
db_url = os.environ.get("DATABASE_URL")

# Get command line arguments (e.g., python script.py data.csv)
filename = sys.argv[1] if len(sys.argv) > 1 else "default.csv"

# Check Python version
print(f"Running on Python {sys.version}")

3. Specialized Data: `collections`

The collections module provides advanced alternatives to standard lists and dictionaries.

Counter: Automatically counts occurrences of items.
defaultdict: A dictionary that creates missing keys automatically.
deque: A list optimized for fast additions/removals from both ends.

from collections import Counter

inventory = ["apple", "banana", "apple", "cherry", "apple"]
stats = Counter(inventory)
print(stats["apple"]) # Output: 3

4. Dates & Times: `datetime`

Handling time is notoriously difficult (time zones, leap years). The datetime module makes it manageable.

from datetime import datetime, timedelta

now = datetime.now()
one_week_later = now + timedelta(weeks=1)

# Format for display
print(now.strftime("%B %d, %Y %H:%M")) # e.g., February 12, 2026 14:30

5. Other “Must-Know” Modules

Module	Purpose
`json`	Read and write JSON data for APIs.
`random`	Generate random numbers and shuffle lists.
`math`	Trigonometry, logarithms, and constants like `pi` and `e`.
`re`	Regular Expressions for advanced text searching.
`hashlib`	Secure hash algorithms (SHA-256) for passwords/data.