An empty list can be defined using square brackets [] or the built-in list() function.

container = list()  # or container = []
container.append(1)
print(container)  # Output: [1]

Lists can hold various data types and can be nested. To access elements in a nested list, use multiple indices.

nested_data = [['apple', 'banana'], [100, 200, 300]]
print(nested_data[0][1])  # Output: banana

Modifying a value is done by assigning a new value to a specific index.

List Operations

Positive Index Slicing

Slicing uses the syntax sequence[start:end:step], with a default step of 1. The slice is "left-closed, right-open".

numbers = [0, 1, 2, 3, 4, 5]
print(numbers[1:3])   # Output: [1, 2]
print(numbers[:3])    # Output: [0, 1, 2]
print(numbers[2:])    # Output: [2, 3, 4, 5]

Negative Index Slicing

Negative indices count from the end of the list.

numbers = [0, 1, 2, 3, 4, 5]
print(numbers[-1])    # Output: 5
print(numbers[-3])    # Output: 3
print(numbers[0:-1])  # Output: [0, 1, 2, 3, 4]

Values at these indices can be modified directly.

List Concatenation, Replication, and Membership

Operator	Description	Example	Result
+	Concatenates two lists	[1, 2] + [3, 4]	[1, 2, 3, 4]
*	Replicates a list	[0] * 3	[0, 0, 0]
in	Checks for membership	5 in [1, 5, 9]	True
not in	Checks for non-membership	3 not in [1, 5, 9]	True

Adding Elements

append() Method

Adds a single element to the end of the list.

data = [0, 1]
data.append(3)
print(data)  # Output: [0, 1, 3]
data.append([2, 4])
print(data)  # Output: [0, 1, 3, [2, 4]]

extend() Method

Adds each element from an iterable to the end of the list. The argument must be iterable.

data = [0, 1]
data.extend([3, 2, 4])
print(data)  # Output: [0, 1, 3, 2, 4]

It works with various iterables like tuples, strings, etc.

data = [0, 1]
my_dict = {'key1': 10, 'key2': 20}
data.extend(my_dict)  # Extends with dictionary keys
print(data)  # Output: [0, 1, 'key1', 'key2']

insert() Method

Inserts an element at a specified index.

items = [0, 1, 2, 3]
items.insert(1, 99)
print(items)  # Output: [0, 99, 1, 2, 3]

Removing Elements

pop() Method

Removes and returns an element at a given index. Defaults to the last element.

values = [0, 1, 2, 3, 4, 5]
last_val = values.pop()
print(values)    # Output: [0, 1, 2, 3, 4]
print(last_val)  # Output: 5
second_val = values.pop(1)
print(values)     # Output: [0, 2, 3, 4]
print(second_val) # Output: 1

remove() Method

Removes the first occurrence of a specified value. Raises an error if the value is not found.

animals = ['cat', 'bat', 'cat', 'rat']
animals.remove('cat')
print(animals)  # Output: ['bat', 'cat', 'rat']

del Statement

Deletes an element at a specific index.

creatures = ['dragon', 'unicorn', 'griffin']
del creatures[1]
print(creatures)  # Output: ['dragon', 'griffin']

Sorting

sort() Method

Sorts the list in-place. Set reverse=True for descending order.

nums = [2, 5, 3.14, 1, -7]
nums.sort()
print(nums)  # Output: [-7, 1, 2, 3.14, 5]
nums.sort(reverse=True)
print(nums)  # Output: [5, 3.14, 2, 1, -7]

reverse() Method

Revreses the list in-place.

nums = [2, 5, 3.14, 1, -7]
nums.reverse()
print(nums)  # Output: [-7, 1, 3.14, 5, 2]

Programming Practices

Removing Duplicates

Using a Set

Convert the list to a set to remove duplicates, then back to a list. Note that this does not preserve order.

source = [0,1,1,1,2,2,3,4,5,5,6,5,3,2,4,6,8,9,2,5]
unique_items = list(set(source))

Using a Loop

Iterate through the list and build a new list with unique elements.

source = [0,1,1,1,2,2,3,4,5,5,6,5,3,2,4,6,8,9,2,5]
result_collection = []
for element in source:
    if element not in result_collection:
        result_collection.append(element)