Python __init__
Summary: in this tutorial, you’ll learn how to use the Python __init__()
method to initialize object’s attributes.
Introduction to the Python __init__() method
When you create a new object of a class, Python automatically calls the __init__()
method to initialize the object’s attributes.
Unlike regular methods, the __init__()
method has two underscores (__) on each side. Therefore, the __init__()
is often called dunder init. The name comes abbreviation of the double underscores init.
The double underscores at both sides of the __init__()
method indicate that Python will use the method internally. In other words, you should not explicitly call this method.
Since Python will automatically call the __init__()
method immediately after creating a new object, you can use the __init__()
method to initialize the object’s attributes.
The following defines the Person
class with the __init__()
method:
class Person:
def __init__(self, name, age):
self.name = name
self.age = ageif __name__ == '__main__':
person = Person('John', 25)
print(f"I'm {person.name}. I'm {person.age} years old.")
Code language: Python (python)
When you create an instance of the Person
class, Python performs two things:
- First, create a new instance of the
Person
class by setting the object’s namespace such as__dict__
attribute to empty ({}
). - Second, call the
__init__
method to initialize the attributes of the newly created object.
Note that the __init__
method doesn’t create the object but only initializes the object’s attributes. Hence, the __init__()
is not a constructor.
If the __init__
has parameters other than the self
, you need to pass the corresponding arguments when creating a new object like the example above. Otherwise, you’ll get an error.
The __init__ method with default parameters
The __init__()
method’s parameters can have default values. For example:
class Person:
def __init__(self, name, age=22):
self.name = name
self.age = ageif __name__ == '__main__':
person = Person('John')
print(f"I'm {person.name}. I'm {person.age} years old.")
Output:
I'm John. I'm 22 years old.
Code language: JavaScript (javascript)
In this example, the age
parameter has a default value of 22
. Because we don’t pass an argument to the Person()
, the age
uses the default value.
Summary
- Use the
__init__()
method to initialize the object’s attributes. - The
__init__()
doesn’t create an object but is automatically called after the object is created.