A list in Python is a sequence data type used for storing a comma-separated collection of objects in a single variable. Lists are always ordered and can contain different types of objects (strings, integers, booleans, etc.). Since they are mutable data types, lists are a good choice for dynamic data (that may be added or removed over time).
# With square brackets list_a =  # With built-in function list_b = list()
Lists can either be defined with square brackets (
) or with the built-in
list() constructor method. In any case, the values initially passed to the new list must be comma-separated.
The following example showcases how lists can hold items of the same type or a mix of different types:
list_1 = [1, 2, 3, 4, 5, 6, 7, 8, 9]list_2 = ["one", 2, "3"]
Stacks and Queues
Python lists can also be made to behave like stacks and queues.
Stacks follow a “last-in, first-out” insertion order. This behavior can be showcased with the
.pop() methods for adding to and removing from the top of the stack, respectively:
stack_example = ["a", "b", "c"]print(stack_example)# Output: ['a', 'b', 'c']stack_example.append(1)stack_example.append(2)stack_example.append(3)print(stack_example)# Output: ['a', 'b', 'c', 1, 2, 3]stack_example.pop()stack_example.pop()print(stack_example)# Output: ['a', 'b', 'c', 1]
Queues follow a “first-in, first-out” insertion order and also utilize the
queue_example = ["a", "b", "c"]print(queue_example)# Output: ['a', 'b', 'c']queue_example.append(1)queue_example.append(2)print(queue_example)# Output: ['a', 'b', 'c', 1, 2]queue_example.pop(0)print(queue_example)# Output: ['b', 'c', 1, 2]
While using a list as a queue is possible, it is not efficient because applying
.pop() to the first item requires shifting all remaining items by one spot and reassigning indices. Instead, a
deque object from the
collections module should be used to efficiently add/remove from a queue.
- Adds an item to end of the list.
- Removes all items from the list.
- Returns a shallow copy of a list.
- Searches a list for a particular item and returns the number of matching entries found.
- Adds list elements to end of the list.
- Finds the first occurence of a particular value within the list.
- Adds an item at a specified index in the list.
- Removes an item from a list while also returning it.
- Removes an item from a list by passing in the value of the item to be removed as an argument.
- Reverse the elements in the list.
- Sorts the contents of the list it is called on.