138 – Alternative constructors as class methods

A common use case for class methods is to provide alternative constructors for classes. (An example from the built-ins is dict.fromkeys.)

A class method accepts the class as its first argument, not self. (Otherwise, it would be an instance method and not a class method.)

class Person:
    def __init__(self, first, last):
        self.first = first
        self.last = last

    @classmethod
    def from_name(cls, name):
        return cls(*name.split())

The class method from_name lets you create instances of the class Person by passing the full name directly:

john = Person.from_name("John Smith")

print(type(john))  # <__main__.Person object at 0x103a26e40>
print(john.first)  # John
print(john.last)  # Smith