摘要：如果對象定義和，則它被認為是數據描述符。屬性查找優先級為類屬性數據描述符實例屬性非數據描述符默認為內部是用實現的，這里用模擬實現功能代碼參考官方文檔原理代碼實現原理代碼實現原理參考資料，知乎如何理解裝飾器，

本人python理論知識遠達不到傳授級別，寫文章主要目的是自我總結，并不能照顧所有人，請見諒，文章結尾貼有相關鏈接可以作為補充

全文分為三個部分裝飾器理論知識、裝飾器應用、裝飾器延申

裝飾理基礎：無參裝飾器、有參裝飾器、functiontools、裝飾器鏈

裝飾器進階：property、staticmethod、classmethod源碼分析（python代碼實現）

"""
假定有一個需求是：打印程序函數運行順序
此案例打印的結果為：
    foo1 function is starting
    foo2 function is starting
"""
from functools import wraps


def NoParamDec(func):
    #函數在被裝飾器裝時后，其函數屬性也會改變，wraps作用就是保證被裝飾函數屬性不變
    @wraps(func)
    def warpper(*args, **kwargs):
        print("{} function is starting".format(func.__name__))
        return func(*args, **kwargs)
    
    return warpper


#python黑魔法省略了NoParamDec=NoParamDec(foo1)
@NoParamDec
def foo1():
    foo2()

@NoParamDec
def foo2():
    pass


if __name__ == "__main__":

    foo1()

"""
假定有一個需求是：檢查函數參數的類型，只允許匹配正確的函數通過程序
此案例打印結果為：
("a", "b", "c")
-----------------------分割線------------------------
ERROS!!!!b must be  
ERROS!!!!c must be  
("a", 2, ["b", "d"])

    
"""
from functools import wraps
from  inspect import signature


def typeAssert(*args, **kwargs):
    deco_args = args
    deco_kwargs = kwargs
    
    def factor(func):
        #python標準模塊類，可以用來檢查函數參數類型，只允許特定類型通過
        sig = signature(func)
        #將函數形式參數和規定類型進行綁定
        check_bind_args = sig.bind_partial(*deco_args, **deco_kwargs).arguments
        
        @wraps(func)
        def wrapper(*args, **kwargs):
            #將實際參數值和形式參數進行綁定
            wrapper_bind_args = sig.bind(*args, **kwargs).arguments.items()
            for name, obj in wrapper_bind_args:
                #遍歷判斷是否實際參數值是規定參數的實例
                if not isinstance(obj, check_bind_args[name]):
                    try:
                        raise TypeError("ERROS!!!!{arg} must be {obj} ".format(**{"arg": name, "obj": check_bind_args[name]}))
                    except Exception as e:
                        print(e)
            return func(*args, **kwargs)
        
        return wrapper
    
    return factor


@typeAssert(str, str, str)
def inspect_type(a, b, c):
    return (a, b, c)


if __name__ == "__main__":
    print(inspect_type("a", "b", "c"))
    print("{:-^50}".format("分割線"))
    print(inspect_type("a", 2, ["b", "d"]))

"""
假定有一個需求是：
輸入類似代碼：
@makebold
@makeitalic
def say():
   return "Hello"

輸出：
Hello
"""
from functools import wraps


def html_deco(tag):
    def decorator(fn):
        @wraps(fn)
        def wrapped(*args, **kwargs):
            return "<{tag}>{fn_result}<{tag}>".format(**{"tag": tag, "fn_result": fn(*args, **kwargs)})
        
        return wrapped
    
    return decorator


@html_deco("b")
@html_deco("i")
def greet(whom=""):
    # 等價于 geet=html_deco("b")(html_deco("i)(geet))
    return "Hello" + (" " + whom) if whom else ""


if __name__ == "__main__":
    print(greet("world"))  # -> Hello world

通常，描述符是具有“綁定行為”的對象屬性，其屬性訪問已經被描述符協議中的方法覆蓋。這些方法是__get__()、__set__()和__delete__()。如果一個對象定義這些方法中的任何一個，它被稱為一個描述符。如果對象定義__get__()和__set__()，則它被認為是數據描述符。僅定義__get__()的描述器稱為非數據描述符（它們通常用于方法，但是其他用途也是可能的）。

屬性查找優先級為：

類屬性

數據描述符

實例屬性

非數據描述符

默認為__getattr__()

class Property(object):
    """
    內部property是用c實現的，這里用python模擬實現property功能
    代碼參考官方doc文檔
    """

    def __init__(self, fget=None, fset=None, fdel=None, doc=None):
        self.fget = fget
        self.fset = fset
        self.fdel = fdel
        self.__doc__ = doc

    def __get__(self, obj, objtype=None):
        if obj is None:
            return self
        if self.fget is None:
            raise (AttributeError, "unreadable attribute")
        print("self={},obj={},objtype={}".format(self,obj,objtype))
        return self.fget(obj)

    def __set__(self, obj, value):
        if self.fset is None:
            raise (AttributeError, "can"t set attribute")
        self.fset(obj, value)

    def __delete__(self, obj):
        if self.fdel is None:
            raise (AttributeError, "can"t delete attribute")
        self.fdel(obj)

    def getter(self, fget):
        return type(self)(fget, self.fset, self.fdel, self.__doc__)

    def setter(self, fset):
        return type(self)(self.fget, fset, self.fdel, self.__doc__)

    def deleter(self, fdel):
        return type(self)(self.fget, self.fset, fdel, self.__doc__)


class Student( object ):
    @Property
    def score( self ):
        return self._score
    @score.setter
    def score( self, val ):
        if not isinstance( val, int ):
            raise ValueError( "score must be an integer!" )
        if val > 100 or val < 0:
            raise ValueError( "score must between 0 ~ 100!" )
        self._score = val


if __name__ == "__main__":
    s = Student()
    s.score = 60   
    s.score         

@staticmethod means: when this method is called, we don"t pass an instance of the class to it (as we normally do with methods). This means you can put a function inside a class but you can"t access the instance of that class (this is useful when your method does not use the instance).

class StaticMethod(object):
    "python代碼實現staticmethod原理"
    
    def __init__(self, f):
        self.f = f
    
    def __get__(self, obj, objtype=None):
        return self.f


class E(object):
    #StaticMethod=StaticMethod(f)
    @StaticMethod
    def f( x):
        return x

if __name__ == "__main__":
    print(E.f("staticMethod Test"))

@staticmethod means: when this method is called, we don"t pass an instance of the class to it (as we normally do with methods). This means you can put a function inside a class but you can"t access the instance of that class (this is useful when your method does not use the instance).

class ClassMethod(object):
    "python代碼實現classmethod原理"
    
    def __init__(self, f):
        self.f = f
    
    def __get__(self, obj, klass=None):
        if klass is None:
            klass = type(obj)
        
        def newfunc(*args):
            return self.f(klass, *args)
        
        return newfunc
    
class E(object):
    #ClassMethod=ClassMethod(f)
    @ClassMethod
    def f(cls,x):
        return x
    
if __name__ == "__main__":
    print(E().f("classMethod Test"))

1, statckoverflow: how to make a chain of decorators

2, python doc:how to descriptor

3，知乎：如何理解裝飾器

4, difference-between-staticmethod-and-classmethod-in-python

5，meaning-of-classmethod-and-staticmethod-for-beginner