Basic list comprehension syntax in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is list comprehension in Python?

List comprehension is a concise way to create lists by writing a single expression inside square brackets, often replacing loops and append calls.

beginner

Write the basic syntax of a list comprehension.

The basic syntax is:
[expression for item in iterable]
where expression is the value to add, item is each element from iterable.

beginner

How does list comprehension compare to a for-loop for creating a list?

List comprehension is shorter and often easier to read. It combines the loop and list creation in one line, unlike a for-loop which needs multiple lines and an append call.

beginner

Example: What does this list comprehension do?
[x * 2 for x in range(3)]

It creates a list by multiplying each number from 0 to 2 by 2. The result is [0, 2, 4].

beginner

Can list comprehensions include conditions?

Yes, but that is a more advanced topic. The basic syntax does not include conditions. Conditions are added with an if clause inside the comprehension.

What is the output of this code?
[x + 1 for x in [1, 2, 3]]

A [2, 3, 4]

B [1, 2, 3]

C [0, 1, 2]

D [1, 3, 5]

Each element is increased by 1, so 1+1=2, 2+1=3, 3+1=4.

Which part of a list comprehension is the 'iterable'?

A The expression before 'for'

B The variable after 'for'

C The brackets []

D The sequence after 'in'

The iterable is the sequence or collection after the 'in' keyword.

What does this list comprehension do?
[x for x in range(5)]

A Creates a list of 5 zeros

B Creates a list of numbers 1 to 5

C Creates a list of numbers 0 to 4

D Creates an empty list

range(5) generates numbers 0 to 4, and the comprehension collects them as is.

Which of these is a valid list comprehension?

A for x in [1, 2, 3]: x * 2

B [x * 2 for x in [1, 2, 3]]

C [x * 2 in [1, 2, 3]]

D x * 2 for x in [1, 2, 3]

Only option B follows the correct list comprehension syntax.

What type of value does a list comprehension produce?

A A list

B A string

C An integer

D A dictionary

List comprehensions always produce a list.

Explain the basic syntax of a list comprehension and how it works.

Think about how you write a for-loop and how list comprehension shortens it.

Give an example of a simple list comprehension that doubles numbers from 0 to 4.

Use range and multiply each item by 2 inside the comprehension.