3.5: Tuple Basics

Learning Objectives

By the end of this section you should be able to

• Describe the features and benefits of a tuple.
• Develop a program that creates and uses a tuple successfully.
• Identify and discuss the mutability of a tuple.

Creating tuples and accessing elements

A tuple is a sequence of comma separated values that can contain elements of different types. A tuple must be created with commas between values, and conventionally the sequence is surrounded by parentheses. Each element is accessed by index, starting with the first element at index 0.

Table 3.4 Example tuples.

tuple_1 = (2, 3, 4) print(f'tuple_1: {tuple_1}') print(tuple_1[1]) print() data_13 = ('Aimee Perry', 96, [94, 100, 97, 93]) print(f'data_13: {data_13}') print(data_13[2])

tuple_1: (2, 3, 4) 3 data_13: ('Aimee Perry', 96, [94, 100, 97, 93]) [94, 100, 97, 93]

Concepts in Practice \(\PageIndex{1}\): Creating tuples and accessing elements

Consider the example above. Which accesses tuple_1's first element?

1. tuple_1[0]
2. tuple_1[1]
3. tuple_1[2]

Answer

a. The first element, 2 , is at index 0.

Concepts in Practice \(\PageIndex{2}\): Creating tuples and accessing elements

Which creates a valid tuple?

1. tuple_2 = (42, 26, 13)
2. tuple_3 = (42, 26, 13.5)
3. both

Answer

c. Tuples can have elements of the same type as well as elements of different types.

Concepts in Practice \(\PageIndex{3}\): Creating tuples and accessing elements

Which creates a tuple with three elements?

1. my_tuple = 'a', 'b', 'c'
2. my_tuple = ['a', 'b', 'c']
3. my_tuple = ('a', 'b', 'c')

Answer

a. A tuple must be created using commas. Parentheses are optional but recommended. The three elements are "a" , "b" , and "c" .

Tuple properties

How do tuples compare to lists? Tuples are ordered and allow duplicates, like lists, but have different mutability. An immutable object cannot be modified after creation. A mutable object can be modified after creation. Tuples are immutable, whereas lists are mutable.

Checkpoint: Mutability of a tuple vs. a list

Concepts in Practice \(\PageIndex{4}\): Using tuples

Consider the final program in the example above. What is the value of my_tuple?

1. (0.693, 0.414, 3.142)
2. (0.693, 1.414, 3.142)
3. Error

Answer

b. my_tuple is initially assigned with the tuple (0.693, 0.414, 3.142). Then my_tuple is assigned with the new tuple, (0.693, 1.414, 3.142), to correct a mistake with the second element.

Concepts in Practice \(\PageIndex{5}\): Using tuples

Why does the following code produce an error?

tuple_1 = ('alpha', 'bravo', 'charlie')
tuple_1.append('charlie')

1. Append isn't allowed.
2. Duplicates aren't allowed.
3. Strings aren't allowed

Answer

a. Tuples are immutable. No changes, including appending, can be made after the tuple is created.

Concepts in Practice \(\PageIndex{6}\): Using tuples

A programmer wants to create a sequence of constants for easy reference that can't be changed anywhere in the program. Which sequence would be the most appropriate?

1. list
2. tuple

Answer

b. Tuples are immutable, so attempted changes produce errors. Using a tuple would protect the constants from accidental changes.

Mutability and performance

Tuples are immutable and have a fixed size, so tuples use less memory. Overall, tuples are faster to create and access, resulting in better performance that can be noticeable with large amounts of data.

Try It: Creating a tuple from a list

Suppose a programmer wants to create a tuple from a list to prevent future changes. The tuple() function creates a tuple from an object like a list. Ex: my_tuple = tuple(my_list) creates a tuple from the list my_list. Update the program below to create a tuple final_grades from the list grades.

Interactive Code

grades = [68, 77, 81, 73]
grades[0] += 5

print(f'final_grades: {final_grades} is a {type(final_grades)}')

Answer

grades = [68, 77, 81, 73]
grades[0] += 5

final_grades = tuple(grades)
print(f'final_grades: {final_grades} is a {type(final_grades)}')

Try It: Creating a tuple with user input

Write a program that reads in two strings and two integers from input and creates a tuple, my_data, with the four values.

Given input:

    x
    y
    15
    20

The output is:

    my_data: ('x', 'y', 15, 20)

Interactive Code

# Read input and create my_data

print(f'my_data: {my_data}')

Input

ft
in
4
11

Answer

str_1 = input()
str_2 = input()
num_1 = int(input())
num_2 = int(input())

my_data = (str_1, str_2, num_1, num_2)
print(f'my_data: {my_data}')