Sequences in Python#

Variables can contain multiple values, those are called sequences. One example we already introduced is a string-typed variable, containing an immutable ordered collection of Unicode items.

The other three basic sequence types are:

Understanding Lists#

Lists are mutable sequences, typically used to store collections of homogeneous typed elements, but elements can also be of mixed types. The elements within a list can be modified after the list is created.

Initialization with Data#

# Creating a list with some elements
my_list = [1, 2, 3, 4, 5]
print("Initialized list:", my_list)

Initialized list: [1, 2, 3, 4, 5]

Accessing Elements#

Entries can be accessed by their index via the bracket operator []. Indices in such sequences start at 0:

# Accessing the first element
first_element = my_list[0]
print("First element:", first_element)

First element: 1

# Accessing the last element using a negative index
last_element = my_list[-1]
print("Last element:", last_element)

Last element: 5

Entries can be changed (lists are mutable) by assigning a new value to an index:

my_list[0] = 10
print("Updated list:", my_list)

Updated list: [10, 2, 3, 4, 5]

Built-in Methods#

The list object provides several methods to work with the underlying data

# Adding an element to the list
my_list.append(6)
print("List after appending 6:", my_list)

List after appending 6: [10, 2, 3, 4, 5, 6]

# Removing an element from the list
my_list.remove(3)
print("List after removing 3:", my_list)

List after removing 3: [10, 2, 4, 5, 6]

# Sorting the list
my_list.sort()
print("Sorted list:", my_list)

Sorted list: [2, 4, 5, 6, 10]

Understanding Tuples#

Tuples are immutable sequences, typically used to store collections of heterogeneous data. Once a tuple is created, its elements cannot be changed.

Initialization with Data#

# Creating a tuple with some elements
my_tuple = (1, 2, 3, 4, 5)
print("Initialized tuple:", my_tuple)

Initialized tuple: (1, 2, 3, 4, 5)

Accessing Elements#

Works just like for lists…

# Accessing the first element
first_element = my_tuple[0]
print("First element:", first_element)

# Accessing the last element
last_element = my_tuple[-1]
print("Last element:", last_element)

First element: 1
Last element: 5

Now try to assign a new value to the first element of the tuple:

Understanding Ranges#

Ranges are immutable collections of numbers, commonly used for counting in loops (later more).

Ranges can be constructed via range(start,end,step), where start defaults to 0, end is not inclusive, and step is an optional parameter for a step width.

Initialization with Data#

# Creating a range of numbers from 0 to 9
my_range = range(10)
print("Initialized range:", list(my_range))

Initialized range: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Accessing Elements#

Works just like for lists…

# Accessing the first element
first_element = my_range[0]
print("First element:", first_element)

# Accessing the last element
last_element = my_range[-1]
print("Last element:", last_element)

First element: 0
Last element: 9

Exercises#

Now that you have learned about lists, tuples, and ranges, try to solve the following exercises to practice your understanding.

  1. Create a list of your favorite fruits. Try to combine it with the numerical list from the top, remember how you did combine strings. Print the result.

  2. Create a tuple with every second number from 0 to 200 and print the last element.