Python List Comprehension
Create Lists

In Python, there's a short and neat way to create new lists. It’s called list comprehension. It looks a little different from what you've seen before, but don't worry — you'll understand it step by step.

What is List Comprehension?

List comprehension is a way to create a new list by doing something to each item in another list (or a range of numbers).

Instead of writing a loop and appending to a list, you can write it all in one line.

Normal Way vs List Comprehension

Let’s first see how we normally make a new list from numbers 1 to 5:

Using a for loop:

numbers = []
for i in range(1, 6):
    numbers.append(i)
print(numbers)

[1, 2, 3, 4, 5]

Now, using list comprehension:

numbers = [i for i in range(1, 6)]
print(numbers)

[1, 2, 3, 4, 5]

Explanation:

• i for i in range(1, 6) means: “for every number i from 1 to 5, take i and put it into the list.”
• The square brackets [ ] mean we’re making a list.

Example 2: Square Each Number

squares = [i*i for i in range(1, 6)]
print(squares)

[1, 4, 9, 16, 25]

Why? Because:

• When i = 1 → 1*1 = 1
• When i = 2 → 2*2 = 4
• ... and so on

Example 3: Double Only Even Numbers

doubles = [i*2 for i in range(1, 6) if i % 2 == 0]
print(doubles)

[4, 8]

Why?

• i % 2 == 0 checks if a number is even
• Only 2 and 4 are even between 1 to 5
• So we double only those: 2→4, 4→8

Example 4: Convert to Uppercase

words = ["apple", "banana", "cherry"]
uppercased = [word.upper() for word in words]
print(uppercased)

['APPLE', 'BANANA', 'CHERRY']

Why?

• word.upper() turns each word into uppercase.
• Each word from the list is transformed and put into a new list.

Example 5: Filter Words Starting with "b"

words = ["apple", "banana", "cherry", "blueberry"]
starts_with_b = [word for word in words if word.startswith("b")]
print(starts_with_b)

['banana', 'blueberry']

Why?

• word.startswith("b") checks if the word starts with the letter “b”.
• Only “banana” and “blueberry” match that rule.

Summary

List comprehension is just a shortcut to make lists. It’s clean and easy once you practice a few times.

Here's the basic pattern to remember:

[expression for item in collection if condition]

You can skip the if part if you don’t need to filter anything.

Next Steps

Try changing the numbers or words in the examples above and see what happens. The best way to learn is by playing around!