List comprehension with condition in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is list comprehension with condition in Python?

It is a way to create a new list by looping over an existing list and including only items that meet a certain condition.

beginner

How do you write a list comprehension that includes only even numbers from a list nums?

Use:
[x for x in nums if x % 2 == 0]
This means: take each x in nums only if x is even.

beginner

What happens if the condition in a list comprehension is always false?

The result is an empty list because no items meet the condition to be included.

intermediate

Can you use multiple conditions in a list comprehension? How?

Yes, by combining conditions with and or or. Example:
[x for x in nums if x > 0 and x % 2 == 0] selects positive even numbers.

beginner

Rewrite this code using list comprehension with condition:

result = []
for x in nums:
    if x > 10:
        result.append(x * 2)

Using list comprehension:

[x * 2 for x in nums if x > 10]

What does this list comprehension do?
[x for x in range(5) if x != 3]

A Creates a list of numbers from 0 to 4 excluding 3

B Creates a list of numbers from 0 to 3

C Creates a list with only the number 3

D Creates an empty list

It loops over numbers 0 to 4 and includes all except 3.

Which of these is a correct syntax for list comprehension with condition?

A [if x > 0 for x in nums]

B [x if x > 0 for x in nums]

C [x for x in nums if x > 0]

D [x for if x > 0 in nums]

The condition comes after the loop: for x in nums if condition.

What will be the output of [x*2 for x in [1,2,3] if x > 2]?

A [2, 4, 6]

B [6]

C [4, 6]

D []

Only 3 is greater than 2, so output is [3*2] = [6].

How can you filter out odd numbers from a list nums using list comprehension?

A [x for x in nums if x < 0]

B [x for x in nums if x % 2 == 1]

C [x for x in nums if x > 0]

D [x for x in nums if x % 2 == 0]

Even numbers satisfy x % 2 == 0, so this keeps evens and filters out odds.

What does the condition part in list comprehension control?

A Which items are included in the new list

B How many times the loop runs

C The order of items in the list

D The type of items in the list

The condition decides if an item should be added to the new list.

Explain how to use list comprehension with a condition to create a list of squares of even numbers from another list.

Think about filtering first, then applying the square.

Describe what happens if the condition in a list comprehension never matches any item.

What does an empty filter mean for the output?