What is a List in Python?
Python lists offer a flexible way to store and manipulate collections of items. In this guide, we’ll delve into Python lists, exploring their methods, and providing examples of how they can be used with arrays. At its core, a Python list is an ordered collection of items. These items can be any of data types - integers, strings, floats, even other lists. Lists are mutable, meaning you can modify them after creation, which make them versatile for various programming tasks.
Creating Lists:
my_list = [1, 2, 3, 4, 5]
# or use list() constructor
my_list2 = list([1, 2, 3, 4, 5])Accessing Elements:
print(my_list[0]) # Output: 1
print(my_list[-1]) # Output: 5
print(my_list2[0]) # Output: 1
print(my_list2[-1]) # Output: 5Python List Methods:
- append(): Adds an item to the end of the list
fruits = ["apple", "banana", "orange"]
fruits.append("grape")
print(fruits)
# Output: ["apple", "banana", "orange", "grape"]- clear(): Clear all elements from the list
fruits = ["orange", "banana", "apple"]
fruits.clear()
print(fruits)
# Output: []- copy(): Returns a copy of the list
fruits = ["apple", "banana", "orange"]
copied_fruits = fruits.copy()
fruits.append("grape")
print(fruits)
# Output: ["apple", "banana", "orange", "grape"]
print(copied_fruits)
# Output: ["apple", "banana", "orange"]- count(): Returns the number of elements with the specified value
fruits = ["apple", "banana", "orange", "apple"]
apple_count = fruits.count("apple")
print(f"There are {apple_count} apples")
# Output: There are 2 apples
orange_count = fruits.count("orange")
print(f"There are {orange_count} orange")
# Output: There are 1 orange- extend(): Extends the list by appending elements from the iterable
fruits = ["apple", "banana", "orange"]
new_fruits = ["grape", "kiwi", "melon"]
fruits.extend(new_fruits)
print(fruits)
# Output: ["apple", "banana", "orange", "grape", "kiwi", "melon"]- index(): Return the index of the first element with the specified value
fruits = ["apple", "banana", "orange", "apple"]
apple_index = fruits.index("apple")
print(f"The first apple is at {apple_index}")
# Output: The first apple is at 0
orange_index = fruits.index("orange")
print(f"The first orange is at {orange_index}")
# Output: The first orange is at 2- insert(): Inserts an element at a specified index
fruits = ["apple", "banana", "orange"]
fruits.insert(1, "grape")
print(fruits)
# Output: ["apple", "grape", "banana", "orange"]- pop(): Removes and return the element at specified index
fruits = ["apple", "banana", "orange"]
popped_fruit = fruits.pop(1)
print("Popped fruit:", popped_fruit)
# Popped fruit: banana
print("Remaining fruits:", fruits)
# Remaining fruits: ["apple", "orange"]- remove(): Removes the first occurrence of a value from the list
fruits = ["apple", "banana", "orange", "banana"]
fruits.remove("banana")
print(fruits)
# Output: ["apple", "orange", "banana"]- reverse(): Reverses the order of the elements in the list
fruits = ["apple", "banana", "orange"]
fruits.reverse()
print(fruits)
# Output: ["orange", "banana", "apple"]- sort(): Sorts the elements of the list in ascending order by default
fruits = ["orange", "banana", "apple"]
fruits.sort()
print(fruits)
# Output: ["apple", "banana", "orange"]Extras
- Differences between
append()andextend()when adding a list as an item:
# append():
existing_array_append = [1, 2]
new_array_append = [6, 7, 8]
existing_array_append.append(new_array_append)
# extend():
existing_array_extend = [1, 2]
new_array_extend = [6, 7, 8]
existing_array_extend.extend(new_array_extend)
print("Using append():", existing_array_append)
# Using append(): [1, 2, [6, 7, 8]]
print("Using extend():", existing_array_extend)
# Using extend(): [1, 2, 6, 7, 8]- Can use one-liner to create a list
nums = [num**2 for num in range(1, 6)]
print(nums)
# Output: [1, 4, 9, 16, 25]
# This is equal to the above
nums = []
for num in range(1, 6):
nums.append(num ** 2)
print(nums)
# Output: [1, 4, 9, 16, 25]Resources
5.1. More on Lists - Python docs
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