Python basics – Day 20

Day 20 – Python Standard Library

Project: Build a “Utility Toolkit” using core Python standard modules (math, random, datetime, time, os).

01. Learning Goal

By the end of this lesson, you will be able to:

• Use Python’s built-in standard libraries effectively
• Perform mathematical operations with math
• Generate random numbers with random
• Work with dates and time using datetime and time
• Manage files and folders with os

02. Problem Scenario

You’re developing a small automation program and need tools for math calculations, random data generation, time management, and file handling — all without installing extra libraries.

Luckily, Python’s Standard Library already provides everything you need.

03. Step 1 – math module (Mathematical Operations)

Provides mathematical functions like square roots, powers, factorials, and constants such as π.

import math

print(math.sqrt(16))    # Square root
print(math.pow(2, 3))   # Power
print(math.factorial(5)) # Factorial
print(math.pi)          # Pi constant

print(math.ceil(3.2))   # Ceiling (round up)
print(math.floor(3.9))  # Floor (round down)

04. Step 2 – random module (Random Number Generation)

Generate random integers, choices, or samples — useful for games, simulations, and testing.

import random

print(random.randint(1, 6))               # Random integer (1–6)
print(random.choice(["Apple", "Banana", "Grape"]))  # Random choice
print(random.sample(range(1, 46), 6))    # Lotto numbers

05. Step 3 – datetime module (Date and Time Handling)

Work with current dates, format conversions, and time calculations.

from datetime import datetime, timedelta

now = datetime.now()
print("Now:", now)

d = datetime(2025, 1, 1, 9, 0)
print("Specific Date:", d)

tomorrow = now + timedelta(days=1)
print("Tomorrow:", tomorrow)

date_str = "2025-09-11 18:30"
dt = datetime.strptime(date_str, "%Y-%m-%d %H:%M")
print("Parsed:", dt)

print(dt.strftime("%Y-%m-%d %H:%M"))
print(dt.strftime("%Y년 %m월 %d일 %H시 %M분"))

06. Step 4 – time module (Delay and Execution Control)

Pause your program or measure execution duration.

import time

print("Wait 3 seconds...")
time.sleep(3)
print("Done!")

07. Step 5 – os module (Operating System Interaction)

Manage files, folders, and paths.

import os

print("Current Working Directory:", os.getcwd())
os.mkdir("test_folder")
os.rmdir("test_folder")

08. Step 6 – Practice Examples

Example 1: Circle Area Calculator

import math

r = 5
area = math.pi * r**2
print("Circle Area:", area)

Example 2: Lotto Number Generator

import random

lotto = random.sample(range(1, 46), 6)
print("Lotto Numbers:", lotto)

Example 3: Today’s Date Formatter

from datetime import datetime

today = datetime.today()
print("Today:", today.strftime("%Y-%m-%d"))

09. Step 7 – Mini Project: Utility Toolkit

Combine all modules into one useful “Utility Toolkit”.

import math, random, time, os
from datetime import datetime

print("--- Utility Toolkit ---")

# 1. Math
r = 4
print("Circle Area:", math.pi * r**2)

# 2. Random
numbers = random.sample(range(1, 46), 6)
print("Random Numbers:", numbers)

# 3. Date & Time
print("Now:", datetime.now().strftime("%Y-%m-%d %H:%M"))

# 4. Delay Example
print("Processing...")
time.sleep(2)
print("Done!")

# 5. OS
print("Current Folder:", os.getcwd())

Output example:

--- Utility Toolkit ---
Circle Area: 50.26548245743669
Random Numbers: [8, 21, 34, 45, 12, 3]
Now: 2025-10-04 16:10
Processing...
Done!
Current Folder: /Users/sabin/projects

10. Reflection

You have learned how to:

• Use core modules (math, random, datetime, time, os)
• Format and calculate with dates
• Generate random sequences and delays
• Interact with your file system safely
• Build a complete Utility Toolkit using only built-in Python features

Next → Day 21 – External Libraries (pip, requests)
Learn how to install and use third-party packages to extend Python’s power.