Dict comprehension

Learn dict comprehensions with {k: v for ...}.

Dict comprehension

A dict comprehension is a short way to build a dict in one line:

squares = {n: n * n for n in [1, 2, 3]}
# {1: 1, 2: 4, 3: 9}

The shape is: {key: value for variable in list}. You can add a filter with if condition at the end. This is shorter and more readable than a classic loop.

If a key appears twice, the later value overwrites the earlier one.

Filtered dict comprehension

You can filter pairs by adding if to a dict comprehension:

even_squares = {n: n * n for n in [1, 2, 3, 4] if n % 2 == 0}
# {2: 4, 4: 16}

This is the same filter logic as in a list comprehension: only items matching the condition enter the result.

On big datasets this method is very short and fast.

Exercise Write a squares dict

Assign to squares a dict comprehension that holds n: n * n pairs for each n in [1, 2, 3, 4]. Then print print(squares).

Show example solution

squares = {n: n * n for n in [1, 2, 3, 4]}
print(squares)

Test yourself

Complete the dict comprehension

squares = {n: n * ____ for n in [1, 2, 3]}

Show answer

squares = {n: n * n for n in [1, 2, 3]}

What does {n: n * 2 for n in [1, 2, 3]} produce?
- [2, 4, 6]
- {2, 4, 6}
- {1: 2, 2: 4, 3: 6}
- (1, 2, 3)
Show answer

{1: 2, 2: 4, 3: 6} — Each n is doubled: {1: 2, 2: 4, 3: 6}.
Match the comprehension types

[...]

List
(...)

Tuple/Generator
{...}

Set/Dict
{k: v}

Dict

Next lesson: Summary - Tuple, set and dict

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies