What is the Walrus Operator in Python?

Often times in python we see while loops that are written like so

def guessing_game(): 
    random_number = random.randint(1, 100)
    user_input = input("guess a number from 1 to 100 : ")
    continue_game = True
    num_of_guess = 3


    while continue_game:
        if int(user_input) == random_number:
            continue_game = False
            print("Congratulations! You guessed the correct number.")
            num_of_guess = 3
     
        if int(user_input) < random_number:
            user_input = input("Too low! Try again: ")

        if int(user_input) > random_number:
            user_input = input("Too high! Try again: ")
        
        if num_of_guess == 0: 
            continue_game = False
            print('Oops, you have exceeded the number of tries.')

        num_of_guess = num_of_guess - 1
     

where we have a Boolean expression that is being evaluated within the while loop, but what if we could assign a variable and evaluate it at the same time, this is where the walrus operator comes in.

The expression assignment operator (also known as the walrus operator) is represented by the symbol := and allows us to assign values to variables as part of an expression.

This allows us to write more concise code by combining assignment and evaluation in a single line. Here is the same while loop using the walrus operator.

def guessing_game(): 
   # with walrus operator
    random_number = random.randint(1, 100)
    while (user_input := input("guess a number from 1 to 100 : ")) != random_number:
        pass

Now you might be wondering when to use the walrus operator, here are some use cases are in while loops, list comprehensions, and conditional statements. Here is an example of using the walrus operator in a list comprehension:

# without walrus operator
numbers = [1, 2, 3, 4, 5]
squared_even_numbers = []
for num in numbers:
    squared = num ** 2
    if squared % 2 == 0:
        squared_even_numbers.append(squared)  
    
# with walrus operator
numbers = [1, 2, 3, 4, 5]
squared_even_numbers = [squared for num in numbers if (squared := num ** 2) % 2 == 0]

Now you might be wondering why its called the walrus operator, just turn to head slightly to the left and you will see it looks like a walrus with tusks!

: =