Python Lesson 18: Modules and Packages

Modules are Python files with reusable code. Python comes with hundreds of built-in modules, and you can install thousands more. Never write code that already exists — import it!

Importing Modules

import math
import random
import os

# Use functions from the module
print(math.sqrt(16))     # 4.0
print(math.pi)           # 3.14159...
print(math.ceil(4.3))    # 5
print(math.floor(4.9))   # 4
print(random.randint(1, 10))  # random number 1-10
print(random.choice(["a","b","c"]))  # random item

from … import (specific function)

from math import sqrt, pi
from random import randint, shuffle

# Now use without "math." prefix
print(sqrt(25))    # 5.0
print(pi)          # 3.14159
print(randint(1, 6))  # roll a dice!

Useful Built-in Modules

import datetime
import os
import json
import time

# Date and time
today = datetime.date.today()
print(today)              # 2024-01-15
print(today.year)         # 2024

# File system
print(os.getcwd())        # current directory
print(os.listdir("."))    # list files

# Sleep (pause)
time.sleep(1)             # pause for 1 second

Installing External Packages

# pip is Python's package installer
# Run in Terminal/Command Prompt:

# pip install requests
# pip install pandas
# pip install pillow

# Then use in your code:
# import requests
# response = requests.get("https://api.example.com")

Creating Your Own Module

# File: my_math.py
def add(a, b):
    return a + b

def square(n):
    return n ** 2

PI = 3.14159

# File: main.py (same folder)
import my_math

print(my_math.add(3, 4))    # 7
print(my_math.square(5))    # 25
print(my_math.PI)           # 3.14159