The Random Module

What is the Random Module?

The random module provides functions for generating random numbers and making random selections. It’s perfect for games, quizzes, simulations, and shuffling data.

To use it, you must import it first:

import random

This gives you access to all the random functions like random.choice(), random.shuffle(), etc.

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Random Numbers

`random.randint(a, b)` - Random Integer

Returns a random whole number between a and b (inclusive - both ends included).

import random

# Random number from 1 to 6 (like rolling a die)
die_roll = random.randint(1, 6)
print(die_roll)  # Could be: 1, 2, 3, 4, 5, or 6

# Random number from 1 to 100
score = random.randint(1, 100)
print(score)  # Could be any number from 1 to 100

Use cases:

Simulating dice rolls
Random scores
Random ages
Any random whole number

`random.random()` - Random Decimal

Returns a random decimal number between 0.0 and 1.0 (not including 1.0).

import random

num = random.random()
print(num)  # e.g., 0.7234891, 0.1829374, 0.9123456

# Scale it up for different ranges
percentage = random.random() * 100  # 0.0 to 100.0
print(f"{percentage:.1f}%")  # e.g., 73.2%

`random.uniform(a, b)` - Random Decimal in Range

Returns a random decimal between a and b.

import random

# Random temperature between 15.0 and 30.0
temperature = random.uniform(15.0, 30.0)
print(f"{temperature:.1f}°C")  # e.g., 23.7°C

# Random price between 10.00 and 50.00
price = random.uniform(10.0, 50.0)
print(f"${price:.2f}")  # e.g., $34.89

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Random Selections

`random.choice(sequence)` - Pick One Random Item

Picks one random item from a sequence (list, tuple, or string).

import random

# Random color
colors = ["red", "blue", "green", "yellow"]
random_color = random.choice(colors)
print(random_color)  # e.g., "blue"

# Random letter
letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
random_letter = random.choice(letters)
print(random_letter)  # e.g., "M"

# Random day
days = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")
random_day = random.choice(days)
print(random_day)  # e.g., "Thursday"

`random.sample(sequence, k)` - Pick Multiple Random Items

Picks k random items from a sequence without duplicates.

import random

# Pick 3 random numbers from 1-10 (no repeats)
numbers = list(range(1, 11))  # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
winners = random.sample(numbers, 3)
print(winners)  # e.g., [7, 2, 9]

# Pick 5 random groups
groups = [
    ("John", "Mary"),
    ("Tracy", "Mo", "Sara"),
    ("Mona", "Kevin", "Abdul"),
    ("Lina", "Sandra"),
    ("Issac", "Antony", "Claire"),
    ("Chloe", "James"),
    ("Denise", "Kong", "Enzo")
]

selected_groups = random.sample(groups, 5)
# Returns 5 unique groups (no group appears twice)

Key difference from random.choice():

choice() picks one item
sample(k) picks k unique items

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Shuffling

`random.shuffle(list)` - Randomize Order

Shuffles a list in place (changes the original list).

import random

# Shuffle a deck of cards
cards = ["A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"]
random.shuffle(cards)
print(cards)  # e.g., ['7', 'K', '2', '5', 'A', '9', ...]

# Shuffle flashcards
flashcards = [("Dog", "Hund"), ("Cat", "Katze"), ("House", "Haus")]
random.shuffle(flashcards)
# Now flashcards are in random order

Important: random.shuffle() changes the original list and returns None.

# ❌ Wrong - shuffle returns None!
cards = ["A", "2", "3"]
shuffled = random.shuffle(cards)
print(shuffled)  # None!

# ✅ Correct - shuffle modifies the list
cards = ["A", "2", "3"]
random.shuffle(cards)
print(cards)  # ['3', 'A', '2']

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Sequences vs. Unordered Collections

What Are Sequences?

Sequences are ordered collections where items have positions.

Lists: ["a", "b", "c"]
Tuples: ("a", "b", "c")
Strings: "abc"
Ranges: range(1, 10)

Unordered collections don’t have positions.

Dictionaries: {"a": 1, "b": 2}
Sets: {"a", "b", "c"}

Why This Matters

Many random functions, e.g. shuffle(), choice(), sample() only work with sequences since they need to access items by position (index). Unordered collections such as dictionaries and sets don’t have positions.

import random

# ❌ Doesn't work with dictionaries
flashcards = {"Dog": "Hund", "Cat": "Katze", "House": "Haus"}
random.choice(flashcards)  # TypeError: 'dict' object is not subscriptable

# ❌ Doesn't work with sets
colors = {"red", "blue", "green"}
random.choice(colors)  # TypeError: 'set' object is not subscriptable

Converting unordered collections to sequences

Solution: Convert to a list first!

Converting Sets

import random

# Convert set to list first
colors = {"red", "blue", "green", "yellow"}
random_color = random.choice(list(colors))
print(random_color)  # e.g., "blue"

Converting Dictionaries

import random

flashcards = {"Dog": "Hund", "Cat": "Katze", "House": "Haus"}

# Option 1: Random key
random_key = random.choice(list(flashcards.keys()))
print(random_key)  # e.g., "Cat"

# Option 2: Random value
random_value = random.choice(list(flashcards.values()))
print(random_value)  # e.g., "Katze"

# Option 3: Random (key, value) pair
random_pair = random.choice(list(flashcards.items()))
english, german = random_pair
print(f"{english} = {german}")  # e.g., "Dog = Hund"

Breaking it down:

flashcards = {"Dog": "Hund", "Cat": "Katze"}

# 1. Get dictionary items (not a sequence yet)
items = flashcards.items()
print(type(items))  # <class 'dict_items'>

# 2. Convert to list (now it's a sequence!)
items_list = list(items)
print(type(items_list))  # <class 'list'>
print(items_list)  # [('Dog', 'Hund'), ('Cat', 'Katze')]

# 3. Now random.choice() works!
random_card = random.choice(items_list)
print(random_card)  # e.g., ('Cat', 'Katze')

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Practical Examples

Example 1: Random Flashcard Quiz

import random

flashcards = {
    "Dog": "Hund",
    "Cat": "Katze",
    "House": "Haus",
    "Car": "Auto",
    "Book": "Buch"
}

# Pick 3 random flashcards to practice
num_questions = 3
flashcard_items = list(flashcards.items())
selected_cards = random.sample(flashcard_items, num_questions)

for english, german in selected_cards:
    user_answer = input(f"Translate '{english}': ")
    if user_answer.lower() == german.lower():
        print("Correct! ✓")
    else:
        print(f"Wrong! The answer was '{german}'")

Example 2: Shuffle and Practice All Cards

import random

flashcards = [
    ("Dog", "Hund"),
    ("Cat", "Katze"),
    ("House", "Haus")
]

# Practice all cards in random order
random.shuffle(flashcards)

for english, german in flashcards:
    user_answer = input(f"Translate '{english}': ")
    if user_answer.lower() == german.lower():
        print("Correct! ✓")
    else:
        print(f"Wrong! The answer was '{german}'")

Example 3: Random Number Guessing Game

import random

# Computer picks a random number
secret_number = random.randint(1, 100)
attempts = 0

print("I'm thinking of a number between 1 and 100...")

while True:
    guess = int(input("Your guess: "))
    attempts += 1
    
    if guess < secret_number:
        print("Too low!")
    elif guess > secret_number:
        print("Too high!")
    else:
        print(f"Correct! You got it in {attempts} attempts!")
        break

Example 4: Random Team Generator

import random

students = ["Alice", "Bob", "Charlie", "Diana", "Eve", "Frank"]

# Shuffle students
random.shuffle(students)

# Split into two teams
team_size = len(students) // 2
team1 = students[:team_size]
team2 = students[team_size:]

print(f"Team 1: {', '.join(team1)}")
print(f"Team 2: {', '.join(team2)}")

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Quick Reference

Function	What It Does	Needs Sequence?	Example
`random.randint(a, b)`	Random integer between a and b	No	`random.randint(1, 6)`
`random.random()`	Random decimal 0.0 to 1.0	No	`random.random()`
`random.uniform(a, b)`	Random decimal between a and b	No	`random.uniform(10.0, 20.0)`
`random.choice(seq)`	Pick one random item	Yes	`random.choice([1,2,3])`
`random.sample(seq, k)`	Pick k unique items	Yes	`random.sample([1,2,3], 2)`
`random.shuffle(list)`	Randomize list order	Yes (list only)	`random.shuffle(my_list)`

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Common Mistakes

Mistake 1: Using shuffle() on Dictionaries

# ❌ Wrong - can't shuffle dictionaries
flashcards = {"Dog": "Hund", "Cat": "Katze"}
random.shuffle(flashcards)  # TypeError!

# ✅ Correct - convert to list first
flashcard_list = list(flashcards.items())
random.shuffle(flashcard_list)

Mistake 2: Assigning shuffle() Result

# ❌ Wrong - shuffle returns None
cards = ["A", "2", "3"]
shuffled = random.shuffle(cards)
print(shuffled)  # None!

# ✅ Correct - shuffle modifies the list
cards = ["A", "2", "3"]
random.shuffle(cards)
print(cards)  # ['3', 'A', '2']

Mistake 3: Forgetting to Import

# ❌ Wrong - forgot to import
random.randint(1, 10)  # NameError: name 'random' is not defined

# ✅ Correct
import random
random.randint(1, 10)

Mistake 4: Using choice() Without list()

# ❌ Wrong - dict.items() is not a list
flashcards = {"Dog": "Hund"}
random.choice(flashcards.items())  # TypeError!

# ✅ Correct - convert to list
random.choice(list(flashcards.items()))

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Summary

Key points:

Import first: import random
Sequences required: choice(), sample(), and shuffle() only work with sequences (lists, tuples, strings)
Convert dictionaries/sets: Use list() to convert before using random functions
- list(dict.keys()) - list of keys
- list(dict.values()) - list of values
- list(dict.items()) - list of (key, value) pairs
shuffle() modifies in place: Doesn’t return anything
sample() for unique items: No duplicates in the selection

Most useful for beginners:

random.randint() - Random whole numbers
random.choice() - Pick one random item
random.sample() - Pick multiple unique items
random.shuffle() - Randomize order

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The Random Module

What is the Random Module?

Random Numbers

random.randint(a, b) - Random Integer

random.random() - Random Decimal

random.uniform(a, b) - Random Decimal in Range

Random Selections

random.choice(sequence) - Pick One Random Item

random.sample(sequence, k) - Pick Multiple Random Items

Shuffling

random.shuffle(list) - Randomize Order

Sequences vs. Unordered Collections

What Are Sequences?

Why This Matters

Converting unordered collections to sequences

Converting Sets

Converting Dictionaries

Practical Examples

Example 1: Random Flashcard Quiz

Example 2: Shuffle and Practice All Cards

Example 3: Random Number Guessing Game

Example 4: Random Team Generator

Quick Reference

Common Mistakes

Mistake 1: Using shuffle() on Dictionaries

Mistake 2: Assigning shuffle() Result

Mistake 3: Forgetting to Import

Mistake 4: Using choice() Without list()

Summary

`random.randint(a, b)` - Random Integer

`random.random()` - Random Decimal

`random.uniform(a, b)` - Random Decimal in Range

`random.choice(sequence)` - Pick One Random Item

`random.sample(sequence, k)` - Pick Multiple Random Items

`random.shuffle(list)` - Randomize Order