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

Recall & Review

beginner

What is dictionary comprehension in Python?

Dictionary comprehension is a concise way to create dictionaries by writing an expression inside curly braces, using a loop and optionally a condition.

beginner

How do you add a condition in a dictionary comprehension?

You add an if statement after the for loop inside the comprehension to filter which items are included.

beginner

Example: What does this code do?

{x: x*x for x in range(5) if x % 2 == 0}

It creates a dictionary with keys as even numbers from 0 to 4, and values as their squares. Result: {0: 0, 2: 4, 4: 16}

intermediate

Can dictionary comprehension with condition replace loops?

Yes, it can replace loops for creating dictionaries when you want to filter items, making code shorter and easier to read.

beginner

What happens if the condition in dictionary comprehension is always false?

The resulting dictionary will be empty because no items meet the condition to be included.

Which part of this dictionary comprehension is the condition?

{k: v for k, v in data.items() if v > 10}

A if v > 10

B for k, v in data.items()

C k: v

D data.items()

The condition filters items where the value is greater than 10.

What will this code output?

{i: i+1 for i in range(3) if i == 5}

A {}

B {5: 6}

C {0: 1, 1: 2, 2: 3}

D Error

No number in range(3) equals 5, so the dictionary is empty.

How do you write a dictionary comprehension that includes only keys that start with 'a' from a dictionary d?

A {k: v for v in d.values() if v.startswith('a')}

B {k: v for k, v in d.items() if v.startswith('a')}

C {k: v for k, v in d.items() if k.startswith('a')}

D {k: v for k in d if k == 'a'}

The condition filters keys starting with 'a'.

Which of these is NOT a valid use of condition in dictionary comprehension?

A Filtering items to include

B Changing keys based on condition

C Adding multiple conditions with 'and' or 'or'

D Using condition outside the comprehension braces

Conditions must be inside the comprehension braces, after the for loop.

What does this dictionary comprehension do?

{x: x**2 for x in range(6) if x % 2 != 0}

A Creates squares of even numbers from 0 to 5

B Creates squares of odd numbers from 0 to 5

C Creates squares of all numbers from 0 to 5

D Creates squares of numbers divisible by 2

The condition x % 2 != 0 selects odd numbers.

Explain how to create a dictionary comprehension with a condition to include only items where the value is greater than 10.

Think about filtering items while creating the dictionary.

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

What does an empty filter produce?