Filtered comprehension

Learn filtered comprehensions with [x for x in xs if cond].

Filtered comprehension

You can filter items by adding an if condition to the comprehension:

evens = [n for n in [1, 2, 3, 4] if n % 2 == 0]
# [2, 4]

The shape is: [expression for variable in list if condition]. Only items whose condition is True stay in the result. The condition is evaluated for each item.

Filtering is shorter than using an if inside a loop to append items.

Multiple conditions

You can combine multiple conditions with and or or:

result = [n for n in range(20) if n % 2 == 0 and n % 3 == 0]
# [0, 6, 12, 18]

Both conditions must be True. This shows that any filtering a loop can do, a comprehension can do too.

Exercise Filter positive numbers

Assign to positives a comprehension that selects items greater than zero from [-3, -1, 0, 2, 5]. Then print print(positives).

Show example solution

positives = [n for n in [-3, -1, 0, 2, 5] if n > 0]
print(positives)

Test yourself

Filter even numbers

evens = [n for n in [1, 2, 3, 4] if n % ____ == 0]

Show answer

evens = [n for n in [1, 2, 3, 4] if n % 2 == 0]

Match the filter parts

if

Filter keyword
n % 2 == 0

Even number condition
and

And connector
or

Or connector
What does [n for n in [1, 2, 3, 4, 5] if n > 3] produce?
- [1, 2, 3]
- [4, 5]
- [3, 4, 5]
- [1, 2]
Show answer

[4, 5] — The condition n > 3 keeps only 4 and 5.

Next lesson: Dict and set comprehension

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