Lists

Object Type Lists

Lists in Python are versatile objects that allow you to store multiple items in a single variable. They are one of the most commonly used data structures in Python due to their flexibility. A list can contain elements of different data types, including numbers, strings, functions, and even other lists. This makes lists ideal for grouping related items together and managing collections of data.

What Are Lists Used For?

Lists are used for a wide variety of tasks in Python programming, such as:

  • Storing Collections of Data: Lists can hold multiple items, making them useful for storing sequences of data like names, numbers, or other collections.
  • Organizing Data: You can organize data into lists to perform operations like sorting, filtering, or iterating through items.
  • Complex Data Structures: Lists can be nested within other lists, allowing you to create complex data structures like matrices or trees.
  • Dynamic : Lists can grow or shrink in size, as you can add, remove, or modify elements at any time.

Creating and Accessing Lists

A list is typically created using square brackets [], with elements separated by commas. Here’s an example:


# Create a list
names = ["Maria", "Evi", "Simon", "Peter"]
numbers = [44,34,5,6]

# Creating a list with multiple elements
mlist = [[2, 5, 3], 21.3, 'Artur']

In this example, mlist contains a sublist [2, 5, 3], a floating-point number 21.3, and an name.

List Methods in Python

Access the elements in the list

You can access list elements using square brackets []. Using single square brackets returns the element while preserving its structure as a list. To access the value inside, you again use [] to access the values

# Accessing elements
print(list1[0])  # Output: [2, 5, 3]
print(list1[1])  # Output: 21.3
print(list1[2])  # Output: <built-in function sum>

# Accessing elements within a sublist
print(list1[0][1])  # Output: 5

Modifying

Lists in Python are mutable, meaning you can change their contents after they are created. Here are some examples of modifying lists:

# Modifying an element in the list
list1[1] = 42.0
print(list1)  # Output: [[2, 5, 3], 42.0, <built-in function sum>]

Adding

list1.append("new item")
print(list1)  # Output: [[2, 5, 3], 42.0, <built-in function sum>, 'new item']

Removing an element from the list

list1.remove(42.0)
print(list1)  # Output: [[2, 5, 3], <built-in function sum>, 'new item']

Common List Methods

Method Description
append(x) Adds an item x to the end of the list.
extend(iterable) Extends the list by appending elements from the iterable.
insert(i, x) Inserts an item x at a given position i.
remove(x) Removes the first item from the list whose value is equal to x.
pop([i]) Removes and returns the item at the given position i. If no index is specified, it removes and returns the last item.
clear() Removes all items from the list.
index(x[, start[, end]]) Returns the index of the first item whose value is equal to x. Raises a ValueError if not found.
count(x) Returns the number of times x appears in the list.
sort(key=None, reverse=False) Sorts the items of the list in place.
reverse() Reverses the elements of the list in place.
copy() Returns a shallow copy of the list.

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