Tuples

Immutable lists — for storing fixed data

What is a Tuple?

A tuple is an immutable sequence in Python, similar to a list but cannot be modified after creation.

List vs Tuple

Feature	List	Tuple
Syntax	`[1, 2, 3]`	`(1, 2, 3)`
Mutability	Mutable	Immutable
Speed	Slower	Faster
Usage	Dynamic data	Fixed data

When to use tuples?

Data should not be modified (e.g., coordinates, dates)
As dictionary keys (lists cannot)
Functions returning multiple values

Creating Tuples

1. Basic Creation

python

# Empty tuple
empty_tuple = ()

# Single element (note the comma!)
single = (5,)  # ✅ This is a tuple
not_tuple = (5)  # ❌ This is just the number 5

# Multiple elements
coordinates = (10, 20)
student_info = ("Alice", 25, "Economics")

# Without parentheses also works (but not recommended)
point = 10, 20
print(type(point))  # <class 'tuple'>

2. Converting from List

python

ages_list = [25, 30, 35]
ages_tuple = tuple(ages_list)
print(ages_tuple)  # (25, 30, 35)

Accessing Tuple Elements

Indexing and Slicing (same as lists)

python

student = ("Alice", 25, "Economics", 3.85)

# Index access
print(student[0])   # Alice
print(student[-1])  # 3.85

# Slicing
print(student[1:3])  # (25, 'Economics')
print(student[:2])   # ('Alice', 25)

Tuple Unpacking

python

# Basic unpacking
point = (10, 20)
x, y = point
print(f"x={x}, y={y}")  # x=10, y=20

# Multiple variable unpacking
student = ("Alice", 25, "Economics")
name, age, major = student
print(name, age, major)  # Alice 25 Economics

# Partial unpacking (using *)
scores = (85, 90, 78, 92, 88)
first, second, *rest = scores
print(first)   # 85
print(second)  # 90
print(rest)    # [78, 92, 88] (Note: rest is a list!)

Social Science Application:

python

# Survey data: (ID, gender, age, income)
respondent = (1001, "Female", 30, 75000)

# Unpack
resp_id, gender, age, income = respondent
print(f"Respondent {resp_id}: {gender}, {age} years old, income ${income:,}")

Tuple Immutability

python

student = ("Alice", 25, "Economics")

# ❌ Cannot modify
student[1] = 26  # TypeError: 'tuple' object does not support item assignment

# ❌ Cannot append
student.append("GPA")  # AttributeError: 'tuple' object has no attribute 'append'

# ❌ Cannot delete
del student[0]  # TypeError

# ✅ Can replace entire tuple
student = ("Bob", 28, "Sociology")

Why immutability?

Prevent accidental modification of important data
Can be used as dictionary keys
Better performance

Tuple Operations

1. Basic Operations

python

numbers = (1, 2, 3, 4, 5, 2, 3)

# Length
print(len(numbers))  # 7

# Max/min/sum
print(max(numbers))  # 5
print(min(numbers))  # 1
print(sum(numbers))  # 20

# Count
print(numbers.count(2))  # 2

# Find index
print(numbers.index(3))  # 2 (first occurrence)

# Check existence
print(2 in numbers)  # True

2. Concatenation and Repetition

python

tuple1 = (1, 2, 3)
tuple2 = (4, 5, 6)

# Concatenation
combined = tuple1 + tuple2
print(combined)  # (1, 2, 3, 4, 5, 6)

# Repetition
repeated = tuple1 * 3
print(repeated)  # (1, 2, 3, 1, 2, 3, 1, 2, 3)

🔬 Real-World Cases

Case 1: Geographic Coordinates

python

# City coordinates (longitude, latitude)
cities = {
    "Beijing": (39.9042, 116.4074),
    "Shanghai": (31.2304, 121.4737),
    "Guangzhou": (23.1291, 113.2644)
}

# Calculate distance between Beijing and Shanghai (simplified)
import math

def calculate_distance(coord1, coord2):
    lat1, lon1 = coord1
    lat2, lon2 = coord2

    # Simplified distance calculation
    distance = math.sqrt((lat2 - lat1)**2 + (lon2 - lon1)**2)
    return distance * 111  # Convert to km (rough)

beijing = cities["Beijing"]
shanghai = cities["Shanghai"]
dist = calculate_distance(beijing, shanghai)
print(f"Distance from Beijing to Shanghai: {dist:.0f} km")

Case 2: Survey Metadata

python

# Survey basic info (should not be modified)
survey_metadata = (
    "China Household Income Survey",  # Survey name
    "2024-01-01",        # Start date
    "2024-12-31",        # End date
    1000,                 # Target sample size
    "Chinese"            # Language
)

# Unpack
name, start_date, end_date, target_n, language = survey_metadata

print(f"=== Survey Information ===")
print(f"Name: {name}")
print(f"Period: {start_date} to {end_date}")
print(f"Target sample: {target_n}")
print(f"Language: {language}")

Case 3: Function Returns Multiple Values

python

def calculate_statistics(data):
    """Calculate descriptive statistics, return tuple"""
    n = len(data)
    mean = sum(data) / n
    sorted_data = sorted(data)
    median = sorted_data[n//2]
    minimum = min(data)
    maximum = max(data)

    return (n, mean, median, minimum, maximum)

# Usage
scores = [85, 92, 78, 90, 88, 76, 95, 82]
n, mean, median, min_val, max_val = calculate_statistics(scores)

print(f"Sample size: {n}")
print(f"Mean: {mean:.2f}")
print(f"Median: {median}")
print(f"Min: {min_val}")
print(f"Max: {max_val}")

🔄 Converting Between Tuples and Lists

python

# List to tuple
ages_list = [25, 30, 35, 40]
ages_tuple = tuple(ages_list)
print(ages_tuple)  # (25, 30, 35, 40)

# Tuple to list
ages_tuple = (25, 30, 35, 40)
ages_list = list(ages_tuple)
print(ages_list)  # [25, 30, 35, 40]

Practical scenario: When you need to modify a tuple

python

# Original tuple
student = ("Alice", 25, "Economics")

# Convert to list to modify
student_list = list(student)
student_list[1] = 26  # Modify age
student = tuple(student_list)  # Convert back to tuple

print(student)  # ('Alice', 26, 'Economics')

🚀 Advanced: Named Tuples (namedtuple)

Problem with regular tuples: Can only access by index, not intuitive.

python

from collections import namedtuple

# Define named tuple
Student = namedtuple('Student', ['name', 'age', 'major', 'gpa'])

# Create instance
alice = Student(name="Alice", age=25, major="Economics", gpa=3.85)

# Access (two ways)
print(alice.name)   # Alice (more intuitive)
print(alice[0])     # Alice (can also use index)

print(alice.gpa)    # 3.85
print(alice[-1])    # 3.85

# Still a tuple, immutable
# alice.age = 26  # ❌ AttributeError

Social Science Application:

python

from collections import namedtuple

# Define survey response structure
Response = namedtuple('Response', [
    'respondent_id',
    'age',
    'gender',
    'income',
    'education',
    'satisfaction'
])

# Create response
resp1 = Response(
    respondent_id=1001,
    age=30,
    gender="Female",
    income=75000,
    education="Bachelor's",
    satisfaction=4
)

# Intuitive access
print(f"Respondent {resp1.respondent_id}:")
print(f"  Age: {resp1.age}")
print(f"  Income: ${resp1.income:,}")
print(f"  Satisfaction: {resp1.satisfaction}/5")

🤔 When to Use List vs Tuple?

Scenario	Use List	Use Tuple
Collect respondent ages	✅ `ages = [25, 30, ...]`	❌
Geographic coordinates	❌	✅ `point = (39.9, 116.4)`
Survey metadata	❌	✅ `metadata = ("Survey", "2024")`
Dynamically add data	✅ `data.append(x)`	❌
Function returns multiple values	❌	✅ `return (mean, std, n)`
As dictionary key	❌	✅ `{(x, y): value}`

Rule of thumb:

Data will change → use list
Data won't change → use tuple

⚠️ Common Errors

Error 1: Forgetting comma for single-element tuple

python

# ❌ Not a tuple
single = (5)
print(type(single))  # <class 'int'>

# ✅ Is a tuple
single = (5,)
print(type(single))  # <class 'tuple'>

Error 2: Trying to modify tuple

python

coords = (10, 20)
coords[0] = 15  # ❌ TypeError: 'tuple' object does not support item assignment

Error 3: Confusing tuple with list

python

# Tuples don't have append method
numbers = (1, 2, 3)
numbers.append(4)  # ❌ AttributeError

# Should use list
numbers = [1, 2, 3]
numbers.append(4)  # ✅

💪 Practice Problems

Exercise 1: RGB Colors

python

# Define several colors (RGB tuples)
red = (255, 0, 0)
green = (0, 255, 0)
blue = (0, 0, 255)

# Tasks:
# 1. Create a function that takes RGB tuple, returns color name
# 2. Calculate "distance" between red and green (Euclidean distance)

Exercise 2: Student Records

python

# Use named tuples to create student record system
# Fields: id, name, age, major, gpa
# Create 3 students, calculate average GPA

Exercise 3: Function Returns Multiple Values

python

# Write function to calculate income quartiles
incomes = [45000, 50000, 60000, 75000, 80000, 95000, 120000, 150000]

# Function returns (Q1, Q2, Q3) as tuple
# Hint: Sort and take 25%, 50%, 75% positions

📚 Next Steps

In the next section, we'll learn about Dictionaries, one of Python's most powerful data structures, similar to R's named list.

Keep moving forward!

Tuples ​

What is a Tuple? ​

List vs Tuple ​

Creating Tuples ​

1. Basic Creation ​

2. Converting from List ​

Accessing Tuple Elements ​

Indexing and Slicing (same as lists) ​

Tuple Unpacking ​

Tuple Immutability ​

Tuple Operations ​

1. Basic Operations ​

2. Concatenation and Repetition ​

🔬 Real-World Cases ​

Case 1: Geographic Coordinates ​

Case 2: Survey Metadata ​

Case 3: Function Returns Multiple Values ​

🔄 Converting Between Tuples and Lists ​

🚀 Advanced: Named Tuples (namedtuple) ​

🤔 When to Use List vs Tuple? ​

⚠️ Common Errors ​

Error 1: Forgetting comma for single-element tuple ​

Error 2: Trying to modify tuple ​

Error 3: Confusing tuple with list ​

💪 Practice Problems ​

Exercise 1: RGB Colors ​

Exercise 2: Student Records ​

Exercise 3: Function Returns Multiple Values ​

📚 Next Steps ​

Tuples

What is a Tuple?

List vs Tuple

Creating Tuples

1. Basic Creation

2. Converting from List

Accessing Tuple Elements

Indexing and Slicing (same as lists)

Tuple Unpacking

Tuple Immutability

Tuple Operations

1. Basic Operations

2. Concatenation and Repetition

🔬 Real-World Cases

Case 1: Geographic Coordinates

Case 2: Survey Metadata

Case 3: Function Returns Multiple Values

🔄 Converting Between Tuples and Lists

🚀 Advanced: Named Tuples (namedtuple)

🤔 When to Use List vs Tuple?

⚠️ Common Errors

Error 1: Forgetting comma for single-element tuple

Error 2: Trying to modify tuple

Error 3: Confusing tuple with list

💪 Practice Problems

Exercise 1: RGB Colors

Exercise 2: Student Records

Exercise 3: Function Returns Multiple Values

📚 Next Steps