init is a method used in Python to initialize object properties. 1. When creating an instance of the class, __init__ is automatically executed, which is used to set the initial state of the object, such as binding the parameter to the instance through self.name = name. 2. You can set default values for parameters, such as breed="Unknown" and age=1 in the Dog class, making initialization more flexible. 3. Logical verification can be added to init, such as the BankAccount class checks whether balance is negative, improving data security. 4. Note that init is an initialization method rather than a constructor. The object already exists before the method is executed and must be spelled correctly and cannot be written as int or init___. Proper use of __init allows classes to have flexible and robust initial configuration when instantiating, thereby effectively managing object state.

__init__ is a constructor of a class in Python that is used to initialize properties when creating an object. Here is a simple and practical example to help you understand how to use __init__ correctly.

What is __init__ ?

When you create an instance of a class, the __init__ method is automatically executed to set the initial state of the object (such as assignment properties).

Basic usage example: Defining a person's class

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

# Create instance person1 = Person("Alice", 30)
person2 = Person("Bob", 25)

print(person1.name, person1.age) # Output: Alice 30
print(person2.name, person2.age) # Output: Bob 25

? illustrate:

• __init__ receives self (representing the instance itself), name and age as parameters.
• self.name and self.age bind values to instances, which can be accessed through instances later.

__init__ with default value

You can also set default values for parameters to make initialization more flexible.

 class Dog:
    def __init__(self, name, breed="Unknown", age=1):
        self.name = name
        self.breed = breed
        self.age = age

# Use the default value dog1 = Dog("Buddy")
dog2 = Dog("Max", "Golden Retriever", 5)

print(dog1.name, dog1.breed, dog1.age) # Buddy Unknown 1
print(dog2.name, dog2.breed, dog2.age) # Max Golden Retriever 5

In this way, even if certain parameters are not passed, there will be no errors.

Type checking or initialization logic in __init__

You can add simple verification or processing logic to __init__ :

 class BankAccount:
    def __init__(self, owner, balance=0):
        self.owner = owner
        if balance < 0:
            raise ValueError("Balance cannot be negative")
        self.balance = balance

    def deposit(self, amount):
        self.balance = amount

    def withdraw(self, amount):
        if amount > self.balance:
            raise ValueError("Insufficient balance")
        self.balance -= amount

# Use example account = BankAccount("Zhang San", 100)
account.deposit(50)
account.withdraw(30)
print(account.balance) # 120

In this example, __init__ not only assigns values, but also performs data legality checks.

Things to note

• __init__ is not a "constructor", but a "initialization method". The object is created before __init__ is executed.
• Do not write it as __int__ or __init___ , the spelling must be correct.
• If the class does not define __init__ , Python will use the parent class's (such as the default object.__init__ ).

Basically that's it. The core of __init__ is: when creating an object, set the initial value . Using it well can make the class more flexible and robust.

The above is the detailed content of python init example. For more information, please follow other related articles on the PHP Chinese website!