Python := Walrus Operator in Python 3.8

The Walrus Operator is a new addition to Python 3.8 and higher. In this article, we're going to discuss the Walrus operator and explain it with an example.

Walrus Operator allows you to assign a value to a variable within an expression. This can be useful when you need to use a value multiple times in a loop, but don't want to repeat the calculation.

The Walrus Operator is represented by the := syntax and can be used in a variety of contexts including while loops and if statements. The Assignment expressions allow a value to be assigned to a variable, even a variable that doesn’t exist yet, in the context of expression rather than as a stand-alone statement.

Code :

numbers = [1, 2, 3, 4, 5]
while (n := len(numbers)) > 0:
    print(numbers.pop())

Output :

Example -

Let's try to understand Assignment Expressions more clearly with the help of an example using both Python 3.7 and Python 3.8. Here we have a list of dictionaries called "sample_data", which contains the userId, name and a boolean called completed.

sample_data = [
    {"userId": 1, "name": "rahul", "completed": False},
    {"userId": 1, "name": "rohit", "completed": False},
    {"userId": 1, "name": "ram", "completed": False},
    {"userId": 1, "name": "ravan", "completed": True}
]
print("With Python 3.8 Walrus Operator:")
for entry in sample_data:
    if name := entry.get("name"):
        print(f'Found name: "{name}"')
print("Without Walrus operator:")
for entry in sample_data:
    name = entry.get("name")
    if name:
        print(f'Found name: "{name}"')

Output:

Here is another example:

## The below example is without Walrus Operator
foods = list()
while True:
  food = input("What food do you like?: ")
  if food == "quit":
    break
  foods.append(food)
# Below Approach uses Walrus Operator
foods1 = list()
while (food := input("What food do you like? (type 'quit' to stop): ")) != "quit":
    foods1.append(food)

Output:

Note: This example, the user input is assigned to the variable name using the Walrus Operator. The value of name is then used in the if statement to determine whether it is in the names list. If it is, the corresponding message is printed, otherwise, a different message is printed.