Regular Methods

Regular methods automatically pass the instance of the class as the first argument, conventionally named self.

class Employee:
    def __init__(self, first, last, pay):
        self.first = first
        self.last = last
        self.pay = pay
        self.email = f'{first}.{last}@company.com'

    def fullname(self):
        return f'{self.first} {self.last}'
    

In the fullname method, self refers to the instance of the Employee class.

Class Methods

Class methods, on the other hand, receive the class itself as the first argument, conventionally named cls. To define a class method, we use the @classmethod decorator.

class Employee:
    raise_amount = 1.04

    def __init__(self, first, last, pay):
        self.first = first
        # ...

    @classmethod
    def set_raise_amount(cls, amount):
        cls.raise_amount = amount
    

Here, set_raise_amount is a class method that modifies the class variable raise_amount

You can call class methods using the class name:

Employee.set_raise_amount(1.05)
print(Employee.raise_amount) # Output: 1.05
    

Class methods are also used as alternative constructors, allowing for different ways to create objects

class Employee:
    # ...

    @classmethod
    def from_string(cls, emp_str):
        first, last, pay = emp_str.split('-')
        return cls(first, last, pay)

emp_str_1 = 'John-Doe-50000'
emp_1 = Employee.from_string(emp_str_1)
print(emp_1.email) # Output: John.Doe@company.com
    

The from_string method parses a string and creates an Employee object.

Static Methods

Static methods do not automatically pass either the instance or the class as the first argument. They are similar to regular functions but are included within a class because they have some logical connection to the class. We use the @staticmethod decorator to define them.

import datetime

class Employee:
    # ...

    @staticmethod
    def is_workday(day):
        # Monday: 0, Sunday: 6
        if day.weekday() == 5 or day.weekday() == 6:
            return False
        return True

my_date = datetime.date(2023, 11, 13) # Monday
print(Employee.is_workday(my_date)) # Output: True
    

The is_workday method checks if a given date is a workday.

Key Differences

• Regular Methods: Automatically take the instance (self) as the first argument.
• Class Methods: Automatically take the class (cls) as the first argument, often used for alternative constructors.
• Static Methods: Do not take the instance or class as the first argument; they are like regular functions within a class.

Conclusion

Understanding when to use regular, class, and static methods is essential for writing clean and efficient Python code. Class methods provide flexibility in object creation, while static methods offer a way to include utility functions within a class context.