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@staticmethod和@classmethod的区别

什么是python的修饰符Decorators？

​ 装饰器模式可以在不影响其他对象的情况下，以动态、透明的方式给单个对象添加职责，也能够处理那些可以撤销的职责。经常用于日志记录、性能测试等场合。

​ 想象一下这个很常见的场景，你写了一个方法：

def A(n):
    if n > 2:
        print n
        print "aaaaaa"
    else:
        print A.__name__
def B(n):
    if n >2:
        print n 
        print "bbbbbb"
    else:
        print B.__name__
if __name__ == '__main__':
    A(3)
    B(3)
#ouptput
3
aaaaaa
3
bbbbbb

用修饰符优美的表达式

def decorator(fn):
    def inner(n):
        if n>2:
            print n
        else:
            print fn.__name__
    return inner
@decorator
def A(n):
    print "aaaaaa"

@decorator
def B(n):
    print "bbbbbb"
if __name__ == '__main__':
    A(3)
    B(3)
# output
3
aaaaaa
3
bbbbbb

当有多个修饰符时候，由远及近影响，如下：

def tag_wrap(tag):
    def decorator(fn):
        def inner(s):
            return '<%s>%s<%s>' % (tag, fn(s), tag)
        return inner
    return decorator
@tag_wrap('a')
@tag_wrap('b')
@tag_wrap('c')
def greet(name):
    return 'Hello, %s!' % name
if __name__ == '__main__':
    print(greet('world'))
#output
<a><b><c>Hello, world!<c><b><a>

我们再举一个日志的例子

def log_calls(fn):

    def inner(*args, **kwargs):
        out = apply(fn, args, kwargs)
        with open('logfile.log', 'a') as logfile:
            logfile.write('%s called with args %s and kwargs %s, returning %s\n' %
        (fn.__name__, args, kwargs, out))
        return out
    return inner

@log_calls
def fizz_buzz_or_number(i):
    if i % 15 == 0:
        return 'fizzbuzz'
    elif i % 3 == 0:
        return 'fizz'
    elif i % 5 == 0:
        return 'buzz'
    else:
        return i
if __name__ == '__main__':
    for i in range(1, 31):
        print(fizz_buzz_or_number(i))
#output
fizz_buzz_or_number called with args (1,) and kwargs {}, returning 1
fizz_buzz_or_number called with args (2,) and kwargs {}, returning 2
fizz_buzz_or_number called with args (3,) and kwargs {}, returning fizz
fizz_buzz_or_number called with args (4,) and kwargs {}, returning 4
fizz_buzz_or_number called with args (5,) and kwargs {}, returning buzz
fizz_buzz_or_number called with args (6,) and kwargs {}, returning fizz
fizz_buzz_or_number called with args (7,) and kwargs {}, returning 7
.
.
.

@staticmethod和@classmethod

Python其实有3个方法,即静态方法(staticmethod),类方法(classmethod)和实例方法

@staticmethod和@classmethod本身也是装饰器的一种特例。先看下面的例子：

def foo(x):
    print "executing foo(%s)"%(x)

class A(object):
    def foo(self,x):
        print "executing foo(%s,%s)"%(self,x)

    @classmethod
    def class_foo(cls,x): #不需要self参数，但第一个参数需要是表示自身类的cls参数
        print "executing class_foo(%s,%s)"%(cls,x)

    @staticmethod
    def static_foo(x): #不需要表示自身对象的self和自身类的cls参数，就跟使用函数一样
        print "executing static_foo(%s)"%x
if __name__ == '__main__':
    a=A()
    a.class_foo(3)
    a.foo(3)
    a.static_foo(3)
    A.class_foo(3)
    A.static_foo(3)
    A.foo(3)
    
#output
executing class_foo(<class '__main__.A'>,3)
executing foo(<__main__.A object at 0x7f79857c9350>,3)
executing static_foo(3)
executing class_foo(<class '__main__.A'>,3)
executing static_foo(3)
A.foo(3)
TypeError: unbound method foo() must be called with A instance as first argument (got int instance instead)

\	实例方法	类方法	静态方法
a = A()	a.foo(x)	a.class_foo(x)	a.static_foo(x)
A	不可用	A.class_foo(x)	A.static_foo(x

参考：

http://pythoncentral.io/difference-between-staticmethod-and-classmethod-in-python/