Python - Standard Library Highlights

Overview

Estimated time: 45–60 minutes

Tour high-impact parts of the standard library you’ll use daily: dates, paths, subprocesses, serialization, and sqlite3.

Learning Objectives

• Use datetime and timezone-safe patterns.
• Manipulate filesystem paths with pathlib.
• Run subprocesses safely and serialize data with json/csv/tomllib.

Prerequisites

• Python - Architecture & Best Practices

datetime

from datetime import datetime, timezone
now = datetime.now(timezone.utc)
print(now.isoformat())

pathlib

from pathlib import Path
p = Path("data") / "file.txt"
print(p.parent, p.name)

subprocess

import subprocess
res = subprocess.run(["echo", "hi"], capture_output=True, text=True, check=True)
print(res.stdout.strip())

Expected Output: hi

tomllib (3.11+)

import tomllib
with open("pyproject.toml", "rb") as f:
    data = tomllib.load(f)
print(type(data))

sqlite3

import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("CREATE TABLE t(x int)")
cur.execute("INSERT INTO t VALUES (42)")
cur.execute("SELECT x FROM t")
print(cur.fetchone()[0])
con.close()

Expected Output: 42

Common Pitfalls

• Naive datetimes without timezone info; prefer timezone-aware (UTC).
• Using shell=True with untrusted input in subprocess; pass a list of args.

Checks for Understanding

1. What’s the advantage of pathlib over os.path?
2. How do you read TOML in Python 3.11+?

Exercises

1. Join a directory and filename with pathlib and print the absolute path.
2. Run a simple command with subprocess and capture output.