Python小知识 - classmethod、staticmethod和正常方法的区别

classmethod、staticmethod和正常方法的区别是什么

简单的创建一个类

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class TestClass(object):
    def method(self):
        return 'instance method called', self

    @classmethod
    def classmethod(self):
        return 'class method called', self

    @staticmethod
    def staticmethod(self):
        return 'static method called', self

接下来实例化类，实现如下

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test = TestClass()
print(test.method())
print(test.classmethod())
print(test.staticmethod())

运行后输出的结果如下

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('instance method called', <__main__.TestClass object at 0x10fe64e50>)
('class method called', <class '__main__.TestClass'>)
Traceback (most recent call last):
  File "/Users/durban/python/practise/main.py", line 31, in <module>
    print(test.staticmethod())
TypeError: staticmethod() missing 1 required positional argument: 'self'

staticmethod这个方法因为加了@staticmethod修饰符导致第一个参数self并不是类自身，而是作为一个参数需要传入

看下面的调用方式

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test = TestClass()
print(test.method())
print(test.classmethod())
print(test.staticmethod(1))

运行后输出的结果如下

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('instance method called', <__main__.TestClass object at 0x105e72e50>)
('class method called', <class '__main__.TestClass'>)
('static method called', 1)

再看个调用方式

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print(TestClass.classmethod())
print(TestClass.staticmethod(1))
print(TestClass.method())

运行后得到的结果类似如下

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('class method called', <class '__main__.TestClass'>)
('static method called', 1)
Traceback (most recent call last):
  File "/Users/durban/python/practise/main.py", line 30, in <module>
    print(TestClass.method())
TypeError: method() missing 1 required positional argument: 'self'

将上面的调用方式调整如下

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print(TestClass.classmethod())
print(TestClass.staticmethod(1))
print(TestClass.method(1))

运行后得到的结果类似如下

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('class method called', <class '__main__.TestClass'>)
('static method called', 1)
('instance method called', 1)

奇怪的是method可以被正常的调用了