用@staticmethod修饰的方法和用@classmethod修饰的方法有什么区别?
当前回答
@staticmethod只是禁用默认函数作为方法描述符。classmethod将函数包装在可调用的容器中,该容器将引用作为第一个参数传递给所属类:
>>> class C(object):
... pass
...
>>> def f():
... pass
...
>>> staticmethod(f).__get__(None, C)
<function f at 0x5c1cf0>
>>> classmethod(f).__get__(None, C)
<bound method type.f of <class '__main__.C'>>
事实上,classmethod有运行时开销,但可以访问所属的类。或者,我建议使用元类并将类方法放在元类上:
>>> class CMeta(type):
... def foo(cls):
... print cls
...
>>> class C(object):
... __metaclass__ = CMeta
...
>>> C.foo()
<class '__main__.C'>
其他回答
实例方法:
+可以修改对象实例状态
+可以修改类状态
类方法:
-无法修改对象实例状态
+可以修改类状态
静态方法:
-无法修改对象实例状态
-无法修改类状态
class MyClass:
'''
Instance method has a mandatory first attribute self which represent the instance itself.
Instance method must be called by a instantiated instance.
'''
def method(self):
return 'instance method called', self
'''
Class method has a mandatory first attribute cls which represent the class itself.
Class method can be called by an instance or by the class directly.
Its most common using scenario is to define a factory method.
'''
@classmethod
def class_method(cls):
return 'class method called', cls
'''
Static method doesn’t have any attributes of instances or the class.
It also can be called by an instance or by the class directly.
Its most common using scenario is to define some helper or utility functions which are closely relative to the class.
'''
@staticmethod
def static_method():
return 'static method called'
obj = MyClass()
print(obj.method())
print(obj.class_method()) # MyClass.class_method()
print(obj.static_method()) # MyClass.static_method()
输出:
('instance method called', <__main__.MyClass object at 0x100fb3940>)
('class method called', <class '__main__.MyClass'>)
static method called
实例方法实际上可以访问对象实例,所以这是我的类对象的一个实例,而使用类方法,我们可以访问类本身。但不适用于任何对象,因为类方法并不真正关心现有的对象。但是,您可以同时调用对象实例上的类方法和静态方法。这将起作用,但实际上并没有什么不同,所以当你在这里调用静态方法时,它会起作用,它会知道你要调用哪个方法。
静态方法用于执行一些实用程序任务,类方法用于工厂方法。工厂方法可以为不同的用例返回类对象。
最后,举一个简短的例子来更好地理解:
class Student:
def __init__(self, first_name, last_name):
self.first_name = first_name
self.last_name = last_name
@classmethod
def get_from_string(cls, name_string: str):
first_name, last_name = name_string.split()
if Student.validate_name(first_name) and Student.validate_name(last_name):
return cls(first_name, last_name)
else:
print('Invalid Names')
@staticmethod
def validate_name(name):
return len(name) <= 10
stackoverflow_student = Student.get_from_string('Name Surname')
print(stackoverflow_student.first_name) # Name
print(stackoverflow_student.last_name) # Surname
我将用一个例子来解释基本的区别。
class A(object):
x = 0
def say_hi(self):
pass
@staticmethod
def say_hi_static():
pass
@classmethod
def say_hi_class(cls):
pass
def run_self(self):
self.x += 1
print self.x # outputs 1
self.say_hi()
self.say_hi_static()
self.say_hi_class()
@staticmethod
def run_static():
print A.x # outputs 0
# A.say_hi() # wrong
A.say_hi_static()
A.say_hi_class()
@classmethod
def run_class(cls):
print cls.x # outputs 0
# cls.say_hi() # wrong
cls.say_hi_static()
cls.say_hi_class()
1-我们可以直接调用静态和类方法,而无需初始化
# A.run_self() # wrong
A.run_static()
A.run_class()
2-静态方法不能调用self方法,但可以调用其他静态和类方法
3-静态方法属于类,根本不会使用对象。
4-类方法不绑定到对象,而是绑定到类。
类方法将类作为隐式第一参数接收,就像实例方法接收实例一样。它是一个绑定到类而不是类的对象的方法。它可以访问类的状态,因为它使用指向类而不是对象实例的类参数。它可以修改将应用于类的所有实例的类状态。例如,它可以修改将适用于所有实例的类变量。
另一方面,与类方法或实例方法相比,静态方法不接收隐式第一个参数。并且无法访问或修改类状态。它只属于类,因为从设计的角度来看,这是正确的方法。但就功能而言,在运行时,它并不与类绑定。
作为指导,使用静态方法作为实用程序,使用类方法作为工厂。或者可以定义一个单例。并使用实例方法对实例的状态和行为进行建模。
希望我清楚!
这是一篇关于这个问题的短文
@staticmethod函数只不过是在类中定义的函数。它可以在不首先实例化类的情况下调用。它的定义通过继承是不可变的。@classmethod函数也可以在不实例化类的情况下调用,但它的定义通过继承遵循子类,而不是父类。这是因为@classmethod函数的第一个参数必须始终是cls(class)。
我的贡献展示了@classmethod、@staticmethod和实例方法之间的区别,包括实例如何间接调用@staticmmethod。但是,与其从实例间接调用@staticmethod,不如将其私有化可能更“Python化”。这里没有演示从私有方法获取内容,但基本上是相同的概念。
#!python3
from os import system
system('cls')
# % % % % % % % % % % % % % % % % % % % %
class DemoClass(object):
# instance methods need a class instance and
# can access the instance through 'self'
def instance_method_1(self):
return 'called from inside the instance_method_1()'
def instance_method_2(self):
# an instance outside the class indirectly calls the static_method
return self.static_method() + ' via instance_method_2()'
# class methods don't need a class instance, they can't access the
# instance (self) but they have access to the class itself via 'cls'
@classmethod
def class_method(cls):
return 'called from inside the class_method()'
# static methods don't have access to 'cls' or 'self', they work like
# regular functions but belong to the class' namespace
@staticmethod
def static_method():
return 'called from inside the static_method()'
# % % % % % % % % % % % % % % % % % % % %
# works even if the class hasn't been instantiated
print(DemoClass.class_method() + '\n')
''' called from inside the class_method() '''
# works even if the class hasn't been instantiated
print(DemoClass.static_method() + '\n')
''' called from inside the static_method() '''
# % % % % % % % % % % % % % % % % % % % %
# >>>>> all methods types can be called on a class instance <<<<<
# instantiate the class
democlassObj = DemoClass()
# call instance_method_1()
print(democlassObj.instance_method_1() + '\n')
''' called from inside the instance_method_1() '''
# # indirectly call static_method through instance_method_2(), there's really no use
# for this since a @staticmethod can be called whether the class has been
# instantiated or not
print(democlassObj.instance_method_2() + '\n')
''' called from inside the static_method() via instance_method_2() '''
# call class_method()
print(democlassObj.class_method() + '\n')
''' called from inside the class_method() '''
# call static_method()
print(democlassObj.static_method())
''' called from inside the static_method() '''
"""
# whether the class is instantiated or not, this doesn't work
print(DemoClass.instance_method_1() + '\n')
'''
TypeError: TypeError: unbound method instancemethod() must be called with
DemoClass instance as first argument (got nothing instead)
'''
"""
推荐文章
- 证书验证失败:无法获得本地颁发者证书
- 当使用pip3安装包时,“Python中的ssl模块不可用”
- 无法切换Python与pyenv
- Python if not == vs if !=
- 如何从scikit-learn决策树中提取决策规则?
- 为什么在Mac OS X v10.9 (Mavericks)的终端中apt-get功能不起作用?
- 将旋转的xtick标签与各自的xtick对齐
- 为什么元组可以包含可变项?
- 如何合并字典的字典?
- 如何创建类属性?
- 不区分大小写的“in”
- 在Python中获取迭代器中的元素个数
- 解析日期字符串并更改格式
- 使用try和。Python中的if
- 如何在Python中获得所有直接子目录