Python Data Structures
Python Lists
A list is an ordered, changeable collection that can hold values of any data type. Lists are one of the most-used data structures in Python.
Creating a List
You create a list by placing comma-separated values inside square brackets and assigning it to a variable. A list can mix data types, though most real-world lists hold items of one kind.
fruits = ["apple", "banana", "mango"]
mixed = [1, "two", 3.0, True]
empty = []
print(fruits)
print(len(fruits))Indexing and Accessing Items
Each item in a list has a position called an index, starting at 0 for the first item. Negative indices count backward from the end, so -1 is always the last item — very handy in loops and functions.
fruits = ["apple", "banana", "mango"]
print(fruits[0]) # apple
print(fruits[-1]) # mango
print(fruits[1:]) # ['banana', 'mango']Lists Are Mutable
Unlike strings and tuples, lists are mutable — you can change, add, or remove elements after creation without making a new list. This makes them ideal for data that grows or shrinks while your program runs.
fruits = ["apple", "banana", "mango"]
fruits[1] = "grape" # change an item
fruits.append("kiwi") # add to the end
fruits.remove("apple") # remove by value
del fruits[0] # remove by index
print(fruits)Nesting Lists
A list can contain other lists, which is useful for grids, matrices, or grouped records. You access an inner item by chaining indices.
matrix = [[1, 2], [3, 4], [5, 6]]
print(matrix[1][0]) # 3When to Use a List
- Storing an ordered collection you plan to loop over, like student names or scores.
- Data that will grow or shrink, such as a shopping cart or task queue.
- Any time order and duplicates matter — use a set instead if you need only unique values.
Use type(x) or the list() function to check or convert other iterables like strings and tuples into a list.
Frequently Asked Questions
What is the difference between a list and an array in Python?+
A Python list can hold mixed data types and resizes automatically, while the built-in array module (and NumPy arrays) store one fixed data type and are more memory-efficient for large numeric datasets.
Are Python lists ordered?+
Yes. Lists keep items in the exact order you insert them, and that order is preserved until you explicitly sort or shuffle the list.
How do I copy a list without affecting the original?+
Use fruits.copy() or fruits[:] to make a shallow copy. Assigning list_b = list_a just creates a second reference to the same list, so changes to one affect the other.