How to Build a List in Python

The problem...

You know what a list is. One variable, multiple values.

But knowing the concept isn't the same as knowing how to build one.

There are several ways to create a list in Python. Each one fits a different situation.

The most common way

You write the values directly, separated by commas, inside square brackets.

squad = ["Raven", "Wolf", "Ghost"]

This is called a list literal. You know the values upfront. You type them in. Done.

It works with any type:

scores = [98, 74, 85]
flags = [True, False, True]
mixed = ["Raven", 98, True]

Starting empty

Sometimes you don't have values yet. You need a list that starts empty and gets filled later.

roster = []

That's it. An empty list is valid. You'll add values to it as your program runs.

You can also use the built-in list() function to create an empty list:

roster = list()

Both do the same thing. [] is more common. You'll see both.

Building from a range

If you need a list of numbers in sequence, you don't type them by hand.

You use range() wrapped in list():

levels = list(range(1, 6))
print(levels)

Output → [1, 2, 3, 4, 5]

range(1, 6) generates numbers from 1 up to — but not including — 6. list() turns that into a list.

even = list(range(0, 11, 2))
print(even)

Output → [0, 2, 4, 6, 8, 10]

The third argument is the step. Here: start at 0, go up to 11, jump by 2.

Converting something else into a list

list() can also turn other things into a list. A string, for example:

letters = list("Bull")
print(letters)

Output → ['B', 'u', 'l', 'l']

Each character becomes a separate element. You won't use this every day, but it's good to know it exists.

The full picture

• ["a", "b", "c"] — list literal, values known upfront
• [] or list() — empty list, values added later
• list(range(n)) — list of numbers in sequence
• list("text") — converts a string into a list of characters

Heads up!

• range() alone is not a list — you need list() to convert it
• list(range(5)) gives you [0, 1, 2, 3, 4] — it starts at 0 by default
• Square brackets create a list — parentheses do not
• An empty list is not an error — it's a tool

The mindset shift

Stop thinking: "I'll figure out how to make the list when I need one."

Start thinking: "Which creation method fits what I'm trying to build?"

What you should understand now

• A list literal uses square brackets with values inside
• An empty list is created with [] or list()
• list(range()) generates a list of numbers without typing them manually
• list() can convert other sequences into a list