What is the purpose of the python classmethod?

2 years ago
William Carter
2 minutes

`classmethod` is a decorator used to define class methods in Python. Unlike instance methods or static methods, class methods can access the class’s attributes and call other class methods without the need to instantiate the class. The `classmethod` decorator binds the class methods to the class and allows them to be called without instantiating the class.

Methods defined with the classmethod decorator are typically used to perform operations related to a class, such as creating alternative methods for creating class instances, returning class attributes, or performing class-level calculations. Common use cases include implementing a factory method for creating objects of a specific type, or serving as helper functions closely related to the class.

Here is an example demonstrating how to define and call a class method using the @classmethod decorator:

class MyClass:
    count = 0

    def __init__(self):
        MyClass.count += 1

    @classmethod
    def get_count(cls):
        return cls.count

# 调用类方法
print(MyClass.get_count())  # 输出：0

# 创建实例
obj1 = MyClass()
obj2 = MyClass()

# 再次调用类方法
print(MyClass.get_count())  # 输出：2

In the example above, get_count is a class method that can be called directly by the class name. Internally, it accesses the class attribute count and returns its value. When creating an instance of the class, the __init__ method increments the value of the count attribute. By calling the get_count method, we can obtain the number of instances of the MyClass class that have been instantiated.

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