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🐍 Python Day 6 Cheat Sheet

Using Modules

📝 Table of Contents

  1. Core Definitions
  2. The random Module
  3. The math Module
  4. The datetime and time Modules
  5. Ways to Import
  6. Quick Reference
  7. Common Mistakes to Avoid

🧠 Core Definitions

  • Module: A file containing Python code (functions, variables, classes) that can be imported and used in other Python files. It's like a toolbox for a specific job.
  • import: The keyword used to bring a module's code into your current program so you can use it.
  • Library: A collection of related modules. The "Python Standard Library" is the collection of modules that comes included with Python.

🎲 The random Module

You must import random before using these functions.

random.randint(a, b)

Returns a random integer N such that a <= N <= b.

import random
roll = random.randint(1, 6)

random.choice(sequence)

Returns a single, random element from a sequence (like a list or tuple).

import random
players = ["Alice", "Bob", "Charlie"]
winner = random.choice(players)

🧮 The math Module

You must import math before using these.

math.sqrt(x)

Returns the square root of a number.

import math
side_length = math.sqrt(144) # 12.0

math.pi

A constant that holds the value of Pi (approx. 3.14159...).

import math
circumference = 2 * math.pi * 5

🕒 The datetime and time Modules

datetime.datetime.now()

Gets the current local date and time.

import datetime
now = datetime.datetime.now()
print(now)

strftime() (String Format Time)

Formats a datetime object into a readable string.

# (continuing from above)
# %Y=Year, %m=month, %d=day, %H=Hour, %M=Minute, %S=Second
formatted = now.strftime("%Y-%m-%d %H:%M:%S")
print(formatted)

time.sleep(seconds)

Pauses the execution of your program for a given number of seconds.

import time
print("Waiting...")
time.sleep(3) # Pauses for 3 seconds
print("Done waiting!")

📥 Ways to Import

Method 1: import module_name (Most Common)

Imports the entire module. You must use the module name as a prefix.

import random
roll = random.randint(1, 6)

Method 2: from module_name import function_name

Imports a specific function directly. No prefix is needed.

from random import choice
winner = choice(["Alice", "Bob"])

Method 3: import module_name as alias

Imports a module and gives it a shorter nickname (alias).

import math as m
circumference = 2 * m.pi * 5

⚡ Quick Reference

Function/Constant Module Description
randint(a, b) random Random integer between a and b.
choice(seq) random Random item from a sequence.
sqrt(x) math Square root of x.
pi math The constant Pi.
datetime.now() datetime The current date and time.
sleep(sec) time Pause the program for sec seconds.

🎯 Common Mistakes to Avoid

❌ Forgetting to import the module.

# Wrong: This will cause a NameError because Python doesn't know 'random'.
roll = random.randint(1, 6)

✅ Always import first.

# Correct
import random
roll = random.randint(1, 6)

❌ Using the wrong prefix after from...import.

# Wrong: 'choice' was imported directly, so it has no prefix.
from random import choice
winner = random.choice(["Alice", "Bob"]) # NameError: name 'random' is not defined

✅ Call the function directly.

# Correct
from random import choice
winner = choice(["Alice", "Bob"])

Happy coding! 🐍✨