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Python List and Tuple

Video link: https://youtu.be/hANUgg72TDc

In this video, we learned about two compound data types in Python: lists and tuples.

Programs in the Video

Python List

Create a List

In Python, a list is a sequence of items in an order. We create lists by placing items inside square brackets [] separated by commas.

A list can contain mixed data type as well as duplicate elements.

# a list of integers
numbers = [1, 5, 6, -4]
print(numbers)

# mixed list
random_list = [2.5, "Hello", -5, 2.5]
print(random_list)

# empty list
list1 = []
print(list1)

Output

[1, 5, 6, -4]
[2.5, 'Hello', -5, 2.5]
[]

We can use the built-in len() function to find length of a list.

# a list of integers
numbers = [1, 5, 6, -4]
print(len(numbers))

# empty list
list1 = []
print(len(list1))

Output

4
0

Access List Elements

A list is a sequence, and its items are always in order.

languages = ["Python", "JavaScript", "C++", "Kotlin"]
print(languages)

Output

['Python', 'JavaScript', 'C++', 'Kotlin']

Here, every elements in the list maintain an order.

We can access individual items of lists by using the item's index. Index starts from 0. So the index of the first item is 0, the second item is 1 and so on.

Item Index
'Python' 0
'JavaScript' 1
'C++' 2
'Kotlin' 3

We can use indices in the following way:

languages = ["Python", "JavaScript", "C++", "Kotlin"]

# first item
print(languages[0])

# third item
print(languages[2])

Output

Python
C++

If the specified index does not exist in the list, Python throws an IndexError exception.

languages = ["Python", "JavaScript", "C++", "Kotlin"]
print(languages[4])

Output

Traceback (most recent call last):
  File "<string>", line 2, in <module>
IndexError: list index out of range

Negative Indexing

In Python, we can also use negative indexing for sequences like lists. Using a negative index gives us items from the last.

Item Index
'Python' -4
'JavaScript' -3
'C++' -2
'Kotlin' -1

Negative index can be used like normal index:

languages = ["Python", "JavaScript", "C++", "Kotlin"]

# last element
print(languages[-1])

# third to last element
print(languages[-3])

Output

Kotlin
JavaScript

Slicing of a List

It is also possible to access a whole section of items from the list, not just a single item.

For example,

languages = ["Python", "JavaScript", "C++", "Kotlin"]

# first three items -> 0, 1, 2
print(languages[0:3])

# second to last items -> 1, 2, 3
print(languages[1:4])

Output

['Python', 'JavaScript', 'C++']
['JavaScript', 'C++', 'Kotlin']

While using slicing, the starting index is inclusive but the ending index is exclusive.

Notes:

  • If we use the empty start index, the slicing starts from the beginning of the list.
  • If we use the empty end index, the slicing ends at the last index.
languages = ["Python", "JavaScript", "C++", "Kotlin"]

# first to third element
print(languages[:3])

# second to last element
print(languages[1:])

Output

['Python', 'JavaScript', 'C++']
['JavaScript', 'C++', 'Kotlin']

Change Items of a List

Lists are mutable. Let's see how we can change items of a list.

For example,

languages = ["Python", "JavaScript", "C++", "Kotlin"]

# modifying the second item
languages[1] = "Ruby"

print(languages)

Output

['Python', 'Ruby', 'C++', 'Kotlin']

We can also modify a range of items of a list.

For example,

languages = ["Python", "JavaScript", "C++", "Kotlin"]

# modifying the second item to third item
languages[1:3] = ["Ruby", "Dart"]

print(languages)

Output

['Python', 'Ruby', 'Dart', 'Kotlin']

in keyword

The in keyword is used to check whether an item is in the list or not.

languages = ["Python", "JavaScript", "C++", "Kotlin"]
print("Python" in languages)

print("Rust" in languages)

Output

True
False

Iterating through a List

If we want to get individual items of a list one by one, we can use a for loop.

languages = ["Python", "JavaScript", "C++", "Kotlin"]

for language in languages:
    print(language)

Output

Python
JavaScript
C++
Kotlin

In each iteration, the value of language is each individual item from the languages list.

List Methods

append() method

To add items to end of the list, we can use the append() method.

languages = ["Python", "JavaScript", "C++", "Kotlin"]
languages.append("Rust")

print(languages)

Output

['Python', 'JavaScript', 'C++', 'Kotlin', 'Rust']

insert() method

To add items to a specified index in the list, we can use the insert() method.

languages = ["Python", "JavaScript", "C++", "Kotlin"]
languages.insert(1, "Rust")

print(languages)

Output

['Python', 'Rust', 'JavaScript', 'C++', 'Kotlin']

remove() method

To remove specified item from a list, we can use the remove() method.

languages = ["Python", "JavaScript", "C++", "Kotlin"]
languages.remove("C++")

print(languages)

Output

['Python', 'JavaScript', 'Kotlin']

copy() method

To create a copy of a list, we can use the copy() method.

languages = ["Python", "JavaScript", "C++", "Kotlin"]

languages1 = languages.copy()
print(languages1)

Output

["Python", "JavaScript", "C++", "Kotlin"]

Python Tuples

A tuple in Python is similar to a list. It is also an ordered collection of items.

The only difference between the two is that lists are mutable (elements of a list can be changed), whereas tuples are immutable (elements of a tuple cannot be changed).

To create a tuple, we need to wrap items inside parentheses () and separate items by a comma.

numbers = (21, -5, 6, 9)
print(numbers)

Output

(21, -5, 6, 9)

We can access elements from a tuple in a similar way to lists.

numbers = (1, 5, 6, 3)
print(numbers[2])

Output

6

We can also perform slicing similar to lists.

numbers = (1, 5, 6, 3)
print(numbers[1:4])

Output

(5, 6, 3)

We can loop through a tuple using a for loop:

numbers = (1, 5, 6, 3)

for number in numbers:
   print(number)

Output

1
5
6
3

Python Tuple vs List

The difference between tuple and list is that a list can be changed but tuple cannot be changed.

Let's try changing an item of a tuple.

languages_tuple = ("Python", "JavaScript", "C++", "Kotlin")
languages_tuple[0] = "Java"
print(languages_tuple)

Output

Traceback (most recent call last):
  File "<string>", line 2, in <module>
TypeError: 'tuple' object does not support item assignment

Programming Task

Can you guess the output of this program?

mixed_list = ["Hello", -34, "Java", True]

print("1.", mixed_list[-1])

mixed_list[1] = "Hi"
print("2.", mixed_list)

mixed_tuple = (1, 3, 4, 5)

mixed_tuple[1] = 100
print("3.", mixed_tuple)

Output

1. True
2. ['Hello', 'Hi', 'Java', True]
Traceback (most recent call last):
File "<string>", line 10, in <module>
TypeError: 'tuple' object does not support item assignment