What I've learned today - 2 - Walrus Operator (:=) in Python

What is?

The new operator allows variable assignments within expressions (also called Walrus Operator). It started as a proposal in PEP572 and became available in Python 3.8.

Benefits

• Make things more compact.
• Compress code when using regular expressions.
• Speed up the processing of large data.
• Code more readable.

Examples

A good example can be found in PEP572 documentation:

• Current:
  

  reductor = dispatch_table.get(cls) if reductor: rv = reductor(x) else: reductor = getattr(x, "__reduce_ex__", None) if reductor: rv = reductor(4) else: reductor = getattr(x, "__reduce__", None) if reductor: rv = reductor() else: raise Error( "un(deep)copyable object of type %s" % cls) 

• Improved:
  

  if reductor := dispatch_table.get(cls): rv = reductor(x) elif reductor := getattr(x, "__reduce_ex__", None): rv = reductor(4) elif reductor := getattr(x, "__reduce__", None): rv = reductor() else: raise Error("un(deep)copyable object of type %s" % cls) 

This code is from python's core, and is a improved version of copy.py

We can use in any condition structure:

# While loop while (command := input("> ")) != "quit": print("You entered:", command) 

# Any if any((comment := line).startswith('#') for line in lines): print("First comment:", comment) else: print("There are no comments") 

# List comprehenssion stuff = [[(f(x) as .y), x/.y] for x in range(5)] # with "as" 

Observations

The operator cannot be used for everything, in some cases he won't work:

a := 1 #INVALID must be done with a=1. a = b := 2 #INVALID must be done with a=b=2 

I appreciate everyone who has read through here, if you guys have anything to add, please leave a comment.