Lists

Learn how to create, access, modify, and manipulate lists in Python. Lists are versatile, ordered collections that can store mixed data types.

Lists in Python

In Python, a list is a very versatile data structure used to store an ordered collection of elements. Lists are mutable, meaning you can modify them after creation, and they can contain elements of different types.

Creating Lists

There are several ways to create lists in Python:

# Empty list
lista_vacia = []

# List with numbers
lista_numeros = [1, 2, 3, 4, 5]

# Mixed data types
lista_mezclada = [1, "dos", 3.0, True]

Lists can contain elements of different types including numbers, strings, booleans, and even other lists.

Accessing Elements

You can access list elements using indices. Python uses zero-based indexing:

lista = ["a", "b", "c", "d", "e"]

# Access first element
primer_elemento = lista[0]     # "a"

# Access last element
ultimo_elemento = lista[-1]    # "e"

# Slicing - get a sublist
sublista = lista[1:4]   # ["b", "c", "d"]

Understanding List Indexing

• Positive indices start from 0 (beginning of list)
• Negative indices start from -1 (end of list)
• lista[start:end] returns elements from start up to (but not including) end

Slicing Shortcuts

• lista[:n] - first n elements
• lista[n:] - from index n to end
• lista[:] - copy of entire list

Modifying Lists

Change Individual Elements

lista = [1, 2, 3, 4, 5]
lista[2] = 10   # Changes the third element to 10
# Result: [1, 2, 10, 4, 5]

Adding Elements

lista = [1, 2, 3]

# Append - adds element to the end
lista.append(4)     # [1, 2, 3, 4]

# Extend - adds multiple elements from another list
lista.extend([5, 6])  # [1, 2, 3, 4, 5, 6]

# Insert - adds element at specific position
lista.insert(2, 10)  # Inserts 10 at index 2

append() adds a single element, while extend() adds all elements from an iterable.

Removing Elements

lista = [1, 2, 3, 4, 5]

# Remove by value - removes first occurrence
lista.remove(3)     # Removes the value 3

# Pop - removes and returns last element (or at specified index)
elemento_eliminado = lista.pop()  # Removes last element

# Delete by index
del lista[2]  # Removes element at index 2

Practical Example: Family Members List

Here’s a real-world example managing a family members list:

miembrosDeLaFamilia = ["tatarabuelo"]
miembrosDeLaFamiliaExpulsado = []

# Adding members
miembrosDeLaFamilia.append("abuelo")
miembrosDeLaFamilia.insert(1, "abuela")
miembrosDeLaFamilia.append("papa")
miembrosDeLaFamilia.append("mama")
miembrosDeLaFamilia.append("yo")

print("ANTES:", miembrosDeLaFamilia)
# Output: ['tatarabuelo', 'abuela', 'abuelo', 'papa', 'mama', 'yo']

# Removing members
del miembrosDeLaFamilia[2]
miembrosDeLaFamilia.remove("abuelo")
miembrosDeLaFamiliaExpulsado.append(miembrosDeLaFamilia.pop(2))

print("DESPUES:", miembrosDeLaFamilia)
print("cantidad de miembros:", len(miembrosDeLaFamilia))
print("miembros expulsado:", miembrosDeLaFamiliaExpulsado)

Sorting Lists

Sort In-Place

The sort() method modifies the original list:

# Sort numbers
numeros = [3, 1, 4, 1, 5, 9, 2]
numeros.sort()
print(numeros)  # [1, 1, 2, 3, 4, 5, 9]

# Sort strings alphabetically
palabras = ["zebra", "manzana", "banana"]
palabras.sort()
print(palabras)  # ['banana', 'manzana', 'zebra']

Sort Without Modifying Original

Use the sorted() function to create a new sorted list:

original = [3, 1, 4]
ordenada = sorted(original)

print(original)  # [3, 1, 4] - unchanged
print(ordenada)  # [1, 3, 4] - new sorted list

sort() modifies the list in-place and returns None. sorted() returns a new sorted list.

Iterating Over Lists

You can loop through list elements using a for loop:

miembrosDeLaFamilia = ["papa", "mama", "yo"]

for miembro in miembrosDeLaFamilia:
    print("#->", miembro.upper())

# Output:
# #-> PAPA
# #-> MAMA
# #-> YO

Common List Operations

Get List Length

lista = [1, 2, 3, 4, 5]
print(len(lista))  # 5

Check if Element Exists

if "manzana" in frutas:
    print("Found!")

Count Occurrences

lista = [1, 2, 2, 3, 2, 4]
print(lista.count(2))  # 3

Find Index of Element

lista = [10, 20, 30, 40]
print(lista.index(30))  # 2

Converting Between Lists and Tuples

You can convert between lists and tuples:

# Tuple to list
tuplaMesclada = ("javier", 234, "javier", "hola mundo")
tuplaMesclada = list(tuplaMesclada)
print(tuplaMesclada)  # Now it's a list

# List to tuple
lista = [1, 2, 3]
tupla = tuple(lista)

Key Takeaways

• Lists are mutable - you can modify them after creation
• Lists are ordered - elements maintain their insertion order
• Lists allow duplicates - the same value can appear multiple times
• Lists can contain mixed types - numbers, strings, booleans, objects, etc.
• Lists support negative indexing - access elements from the end

Use lists when you need a collection that can grow, shrink, or change over time. For fixed collections, consider using tuples instead.