python中 staticmethod与classmethod

class Foo():
    # 无修饰
    def instance_method(self): #传入的第一个参数是self, 即instance本身
        print(‘the first argument of instance_method:‘, self)

    @classmethod
    def class_method(cls): # 传入的第一个参数是class
        print(‘the first argument of class_method:‘, cls)

    @staticmethod
    def static_method(): # 没有默认的首位参数, 只有自定义参数
        print(‘the first argument of static_method:‘)

foo = Foo()
foo.instance_method()
Foo.class_method()
foo.class_method()
Foo.static_method()
foo.static_method()
try:
    Foo.instance_method()
except:
    print(‘instance method can not be accessed through class.‘)

the first argument of instance_method: <__main__.Foo object at 0x7fd135ec3b38>
the first argument of class_method: <class ‘__main__.Foo‘>
the first argument of class_method: <class ‘__main__.Foo‘>
the first argument of static_method:
the first argument of static_method:
instance method can not be accessed through class

class Date:

    def __init__(self,day=0, month=0, year=0):
        self.day=day
        self.month = month
        self.year = year

    @classmethod
    def from_string(cls, date_as_string):
        day, month, year = map(int,date_as_string.split(‘-‘))
        my_date = cls(day, month, year)
        return my_date

    @staticmethod
    def is_date_valid(date_as_string):
        day, month, year = map(int, date_as_string.split(‘-‘))
        return day <= 31 and month <= 12 and year <= 3999


if __name__ == ‘__main__‘:
    my_date = Date.from_string(‘11-09-2012‘)
    print(my_date.day, my_date.month,my_date.year)
    is_date = Date.is_date_valid(‘13-13-2012‘)
    print(is_date)

outputs: 
11 9 2012
False

class A:
    @classmethod
    def cm(cls):
        print(‘类方法cm(cls)调用者：‘, cls.__name__)

    @staticmethod
    def sm():
        print(‘静态方法sm()被调用‘)

class B(A):
    pass

A.cm()  # 类方法cm(cls)调用者： A
B.cm()  # 类方法cm(cls)调用者： B
A.sm()  # 静态方法sm()被调用
B.sm()  # 静态方法sm()被调用

class Kls:
    def __init__(self,data):
        self.data = data
    def printd(self):
        print(self.data)

ik1=Kls(‘arun‘)
ik2=Kls(‘seema‘)
ik1.printd()
ik2.printd()

# 如果现在我们想写一些仅仅与类交互而不是和实例交互的方法会怎么样呢? 我们可以在类外面写一个简单的方法来做这些，
# 但是这样做就扩散了类代码的关系到类定义的外面. 如果像下面这样写就会导致以后代码维护的困难:
def get_no_of_instances(cls_obj):
    return cls_obj.no_inst
class Kls:
    no_inst = 0
    def __init__(self):
        Kls.no_inst = Kls.no_inst + 1
ik1 = Kls()
ik2 = Kls()
print(get_no_of_instances(Kls)) # 2

class Kls(object):
    no_inst = 0
    def __init__(self):
        Kls.no_inst = Kls.no_inst + 1
    @classmethod
    def get_no_of_instance(cls_obj):
        return cls_obj.no_inst
ik1 = Kls()
ik2 = Kls()
print(ik1.get_no_of_instance())
print(Kls.get_no_of_instance())
# 2
# 2