Master the Python walrus operator and unlock new programming skills!

Hello everyone, I am Xianhuan, an old acquaintance of yours!

The walrus is the largest mammal, and some people call it an "indigenous" resident of the northern hemisphere. It has a round head, a short and wide mouth, a thick nose, and the upper canine teeth form tusks that are 40cm-90cm long, each weighing more than 4kg. Male walruses can reach 4 meters in length and weigh 2 tons. Walruses like to live in groups, with thousands of them clustered together.

Walrus eyes are narrowed like an old man lacking energy. They love to sleep in and spend most of their lives lying on the ice. They can also sleep in the water, which is really amazing.

As a 996 roller farmer, I envy their lives very much and really want to lie down like them.

Okay, let’s get down to business, let’s continue rolling! Today I bring you an operator named after a walrus - the walrus operator.

The Python walrus operator was proposed in PEP 572 and incorporated and released in Python 3.8.

The original English name of the Walrus operator is Assignment Expressions, that is, assignment expressions. A walrus expression consists of a : and an =, namely := . We usually call it the walrus operator because it looks like a walrus rotated 90°. The author is very imaginative and can connect all these!

Grammar

The syntax format of the walrus operator is:

(variable_name := expression)

This is a new assignment operator, similar to our common =, a variable name is followed by expression.

Usage

Used for if-else conditional expressions

Conventional writing:

a = 5
if a > 1:
print('do sth!')

Upgrade writing:

if a := 5 > 1:
print('do sth!')

Used for while Loop

Conventional writing method:

n = 3
while n:
print('do sth!')
n -= 1

Upgrade writing method:

n = 3
while (n := n - 1) + 1: 
print('do sth!')

The reason why 1 is added here is because n is decremented by 1 before the output is executed.

Read file

Conventional writing method:

fp = open("test.txt", "r")
while True:
line = fp.readline()
if not line:
break
print(line.strip())
fp.close()

Upgrade writing method:

fp = open("test.txt", "r")
while line := fp.readline():
print(line.strip())

Using the walrus operator in appropriate scenarios can reduce program complexity. Simplifying the code can even improve the performance of the program.

Not Applicable Scenarios

Although the walrus operator is easy to use, it cannot be used in all scenarios, and it still has its limitations.

Variable assignment

We cannot use the = operator with the := operator. The walrus operator can only be part of an expression:

a = 5 # Valid 
a := 5 # InValid 
empty_list = [] # Valid 
empty_list := [] # InValid

If you write like this , the editor will prompt an error directly.

Addition and subtraction

a += 5 # Valid
a :+=5 # Invalid

Assignment expressions in Lambda functions

(lambda: a:= 5) # Invalid
lambda: (a := 5) # Valid, but not useful
(var := lambda: 5) # Valid

Controversy

Keywords

Walrus operator usage: = This keyword is not liked by most developers. This keyword is different from what we usually come into contact with. The creator has a unique approach.

I don’t like this very much, but I respect the creator’s rules. After all, they have brought such practical operators to everyone.

Operator name

Some developers think that the name "walrus operator" is too abstract and cannot clearly express the meaning of this operator. Almost 100% of people see it for the first time. With this name, you wouldn't think of its function.

Brother Huan thinks that since there is no set naming method, it is understandable for the author to choose a meaningful name.

Summary

From now on, we have another conventional weapon in our arsenal. When you are fighting (involving others), don’t forget to use it. It will improve the performance of the program and the simplicity of the code. Sexuality will be improved.

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