Methods and Attributes

A class is a kind of data type, just like a string, integer or list. When we create an object of that data type, we call it an instance of a class. The data values which we store inside an object are called attributes, and the functions which are associated with the object are called methods.

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Example

Here is an example of a simple custom class which stores information about a person. Note the attributes (name, surname, birthdate) and the methods (in this case the method "age")

import datetime # we will use this for date objects

class Person:

    def __init__(self, name, surname, birthdate, address, telephone, email):
        self.name = name
        self.surname = surname
        self.birthdate = birthdate

        self.address = address
        self.telephone = telephone
        self.email = email

    def age(self):
        today = datetime.date.today()
        age = today.year - self.birthdate.year

        if today < datetime.date(today.year, self.birthdate.month, self.birthdate.day):
            age -= 1

        return age

person = Person(
    "Jane",
    "Doe",
    datetime.date(1992, 3, 12), # year, month, day
    "No. 12 Short Street, Greenville",
    "555 456 0987",
    "[email protected]"
)

print(person.name)
print(person.email)
print(person.age())

The __init__() Function

The examples above are classes and objects in their simplest form, and are not really useful in real life applications. To understand the meaning of classes we have to understand the built-in __init__() function. All classes have a function called __init__(), which is always executed when the class is being initiated. Use the __init__() function to assign values to object properties, or other operations that are necessary to do when the object is being created:

Example

Create a class named Person, use the __init__() function to assign values for name and age:

class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

p1 = Person("John", 36)

print(p1.name)
print(p1.age)

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Note: The __init__() function is called automatically every time the class is being used to create a new object.