今天学习，碰到了修饰符'@'，不太了解，查看了下。
简单的整理下：
@dec2@dec1def func(arg1, arg2, ...): pass
等价于
def func(arg1, arg2, ...): passfunc = dec2(dec1(func))
使用示例：
在comp.lang.python 和 python-dev的大部分讨论集中在更简捷地使用内置修饰符staticmethod() 和 classmethod() 上。但修饰符的功能远比这强大。下面会对它的使用进行一些讲解：
1.定义一个执行即退出的函数。注意，这个函数并不像通常情况那样，被真正包裹。
def onexit(f): import atexit atexit.register(f) return f@onexitdef func(): ...
（Note that this example is probably not suitable for real usage, but is for example purposes only.）
2.定义一个只能产生一个实例的类（有实例后，这个类不能再产生新的实例）。注意，一旦这个类失效了(估计意思是保存在下文的singleton中字典中的相应键失效)，就会促使程序员让这个类产生更多的实例。（来自于python-dev的Shane Hathaway）
def singleton(cls): instances = {} def getinstance(): if cls not in instances: instances[cls] = cls() return instances[cls] return getinstance@singletonclass MyClass: ... 3.Add attributes to a function. (Based on an example posted by Anders Munch on python-dev.)
def attrs(**kwds): def decorate(f): for k in kwds: setattr(f, k, kwds[k]) return f return decorate@attrs(versionadded="2.2", author="Guido van Rossum")def mymethod(f): ...
4.Enforce function argument and return types. Note that this copies the func_name attribute from the old to the new function. func_name was made writable in Python 2.4a3:
def accepts(*types): def check_accepts(f): assert len(types) == f.func_code.co_argcount def new_f(*args, **kwds): for (a, t) in zip(args, types): assert isinstance(a, t), \ "arg %r does not match %s" % (a,t) return f(*args, **kwds) new_f.func_name = f.func_name return new_f return check_acceptsdef returns(rtype): def check_returns(f): def new_f(*args, **kwds): result = f(*args, **kwds) assert isinstance(result, rtype), \ "return value %r does not match %s" % (result,rtype) return result new_f.func_name = f.func_name return new_f return check_returns@accepts(int, (int,float))@returns((int,float))def func(arg1, arg2): return arg1 * arg2
5.Declare that a class implements a particular (set of) interface(s). This is from a posting by Bob Ippolito on python-dev based on experience with .
def provides(*interfaces): """ An actual, working, implementation of provides for the current implementation of PyProtocols. Not particularly important for the PEP text. """ def provides(typ): declareImplementation(typ, instancesProvide=interfaces) return typ return providesclass IBar(Interface): """Declare something about IBar here"""@provides(IBar)class Foo(object): """Implement something here..."""