Python裝飾器代碼詳解
一、理解裝飾器
所有東西都是對(duì)象(函數(shù)可以當(dāng)做對(duì)象傳遞)
由于函數(shù)也是一個(gè)對(duì)象，而且函數(shù)對(duì)象可以被賦值給變量，所以，通過變量也能調(diào)用該函數(shù)。
def function_one():
print("測(cè)試函數(shù)")
#可以將一個(gè)函數(shù)賦值給一個(gè)變量，比如
foo =function_one #這里沒有在使用小括號(hào)，因?yàn)槲覀儾⒉皇窃谡{(diào)用function_one函數(shù),而是在將它放在foo變量里。
foo()
'''
測(cè)試函數(shù)
Process finished with exit code 0
'''
閉包的概念:
1）函數(shù)嵌套
2）內(nèi)部函數(shù)使用外部函數(shù)的變量
3）外部函數(shù)的返回值為內(nèi)部函數(shù)
示例：
def outer_function(message):
def inner_function():
print(message)
return inner_function
func = outer_function("你好")
func() #你好
二、裝飾器原型
裝飾器的作用就是 不修改源代碼以及原函數(shù)調(diào)用方式的情況下 給原函數(shù)增加新的功能。
#將函數(shù)作為參數(shù)傳給另一個(gè)函數(shù)
def decorator_function(original_function):
def wrapper_function():
print('wrapper executed this before {}'.format(original_function.__name__))
original_function()
return wrapper_function
'''
返回wrapper_function而不是wrapper_function()；這是因?yàn)楫?dāng)你把一對(duì)小括號(hào)放在后面，這個(gè)函數(shù)就會(huì)執(zhí)行；
然而如果你不放括號(hào)在它后面，那它可以被到處傳遞，并且可以賦值給別的變量而不去執(zhí)行它。
'''
def display():
print('display function ran')
decorator_display = decorator_function(display)
decorator_display()
運(yùn)行結(jié)果：
wrapper executed this before display display function ran Process finished with exit code 0
1、不帶參數(shù)的裝飾器
def decorator_function(original_function):
def wrapper_function():
print('wrapper executed this before {}'.format(original_function.__name__))
original_function()
return wrapper_function
@decorator_function
def display(): #等價(jià)于display =decorator_function(display)
print('display function ran')
display()
運(yùn)行結(jié)果：
wrapper executed this before display
display function ranProcess finished with exit code 0
2.帶參數(shù)的被裝飾的函數(shù)
def decorator_function(original_function):
def wrapper_function(*args,**kwargs):
print('wrapper executed this before {}'.format(original_function.__name__))
original_function(*args,**kwargs)
return wrapper_function
@decorator_function
def display():
print('display function ran')
@decorator_function
def display_info(name,age):
print('display_info ran with arguments ({},{})'.format(name,age))
display()
print('='*50)
display_info('Michal',20)
運(yùn)行結(jié)果：
wrapper executed this before display
display function ran
==================================================
wrapper executed this before display_info
display_info ran with arguments (Michal,20)Process finished with exit code 0
運(yùn)行如下代碼會(huì)出現(xiàn)一個(gè)問題
def decorator_function(original_function):
def wrapper_function(*args,**kwargs):
print('wrapper executed this before {}'.format(original_function.__name__))
original_function(*args,**kwargs)
return wrapper_function
@decorator_function
def display():
print('display function ran')
@decorator_function
def display_info(name,age):
print('display_info ran with arguments ({},{})'.format(name,age))
display_info = decorator_function(display_info)
print(display_info.__name__)
wrapper_function
Process finished with exit code 0
輸出的應(yīng)該是display_info，這里的函數(shù)被wrapper_function替代了，重寫了我們函數(shù)的名字和注釋文檔(docstring)。Python中可以使用functools.wraps來解決這個(gè)問題。
from functools import wraps
def decorator_function(original_function):
@wraps(original_function)
def wrapper_function(*args,**kwargs):
print('wrapper executed this before {}'.format(original_function.__name__))
original_function(*args,**kwargs)
return wrapper_function
@decorator_function
def display():
print('display function ran')
@decorator_function
def display_info(name,age):
print('display_info ran with arguments ({},{})'.format(name,age))
display_info = decorator_function(display_info)
print(display_info.__name__)
運(yùn)行結(jié)果：
display_info
Process finished with exit code 0
3.帶參數(shù)的裝飾器
在函數(shù)中嵌入裝飾器
from functools import wraps def logit(logfile='out.log'): def logging_decorator(func): @wraps(func) def wrapped_function(*args, **kwargs): log_string = func.__name__ + " was called" print(log_string) # 打開logfile，并寫入內(nèi)容 with open(logfile, 'a') as opened_file: # 現(xiàn)在將日志打到指定的logfile opened_file.write(log_string + '\n') return func(*args, **kwargs) return wrapped_function return logging_decorator @logit() def myfunc1(): pass myfunc1() # Output: myfunc1 was called # 現(xiàn)在一個(gè)叫做 out.log 的文件出現(xiàn)了，里面的內(nèi)容就是上面的字符串 @logit(logfile='func2.log') def myfunc2(): pass myfunc2() # Output: myfunc2 was called # 現(xiàn)在一個(gè)叫做 func2.log 的文件出現(xiàn)了，里面的內(nèi)容就是上面的字符串
4.使用類作為裝飾器
class myDecorator(object):
def __init__(self, f):
print("inside myDecorator.__init__()")
f() # Prove that function definition has completed
def __call__(self):
print("inside myDecorator.__call__()")
@myDecorator
def aFunction():
print("inside aFunction()")
print("Finished decorating aFunction()")
aFunction()
運(yùn)行結(jié)果：
inside myDecorator.__init__() inside aFunction() Finished decorating aFunction() inside myDecorator.__call__() Process finished with exit code 0
被裝飾后的函數(shù)aFunction()實(shí)際上已經(jīng)是類myDecorator的對(duì)象。當(dāng)再調(diào)用aFunction()函數(shù)時(shí)，實(shí)際上就是調(diào)用類myDecorator的對(duì)象，因此會(huì)調(diào)用到類myDecorator的__call__()方法。
因此使用類作為裝飾器裝飾函數(shù)來對(duì)函數(shù)添加一些額外的屬性或功能時(shí)，一般會(huì)在類的__init__()方法中記錄傳入的函數(shù)，再在__call__()調(diào)用修飾的函數(shù)及其它額外處理。
class entryExit(object):
def __init__(self, f):
self.f = f
def __call__(self):
print("Entering", self.f.__name__)
self.f()
print("Exited", self.f.__name__)
@entryExit
def func1():
print("inside func1()")
@entryExit
def func2():
print("inside func2()")
func1()
func2()
運(yùn)行結(jié)果：
Entering func1
inside func1()
Exited func1
Entering func2
inside func2()
Exited func2Process finished with exit code 0
5.使用對(duì)象作為裝飾器
空參：
from functools import wraps
class decorator_class:
def __init__(self):
print('執(zhí)行decorator_class類的__init__()方法')
def __call__(self, original_function):
print('執(zhí)行decorator_class類的__call__()方法')
@wraps(original_function)
def wrapped_function(*args, **kwargs):
print('call method executed this before {}'.format(original_function.__name__))
print('執(zhí)行' + original_function.__name__ + '()')
original_function(*args, **kwargs)
print(original_function.__name__ + '()執(zhí)行完畢')
return wrapped_function
@decorator_class()
def display_info(name,age):
print('display_info ran with arguments ({},{})'.format(name,age))
display_info('Michael',20)
運(yùn)行結(jié)果如下：
執(zhí)行decorator_class類的__init__()方法
執(zhí)行decorator_class類的__call__()方法
call method executed this before display_info
執(zhí)行display_info()
display_info ran with arguments (Michael,20)
display_info()執(zhí)行完畢Process finished with exit code 0
帶參數(shù)：
from functools import wraps
class decorator_class:
def __init__(self,arg1, arg2):
print('執(zhí)行decorator_class類的__init__()方法')
self.arg1 =arg1
self.arg2=arg2
def __call__(self, original_function):
print('執(zhí)行decorator_class類的__call__()方法')
@wraps(original_function)
def wrapped_function(*args, **kwargs):
print('執(zhí)行wrapped_function()')
print('call method executed this before {}'.format(original_function.__name__))
print('裝飾器參數(shù)：', self.arg1, self.arg2)
print('執(zhí)行' + original_function.__name__ + '()')
original_function(*args, **kwargs)
print(original_function.__name__ + '()執(zhí)行完畢')
return wrapped_function
@decorator_class('Hello', 'World')
def display_info(name,age):
print('display_info ran with arguments ({},{})'.format(name,age))
display_info('Michael',20)
運(yùn)行結(jié)果如下：
執(zhí)行decorator_class類的__init__()方法
執(zhí)行decorator_class類的__call__()方法
執(zhí)行wrapped_function()
call method executed this before display_info
裝飾器參數(shù)： Hello World
執(zhí)行display_info()
display_info ran with arguments (Michael,20)
display_info()執(zhí)行完畢Process finished with exit code 0
示例2：
from functools import wraps class logit(object): def __init__(self, logfile='out.log'): self.logfile = logfile def __call__(self, func): @wraps(func) def wrapped_function(*args, **kwargs): log_string = func.__name__ + " was called" print(log_string) # 打開logfile并寫入 with open(self.logfile, 'a') as opened_file: # 現(xiàn)在將日志打到指定的文件 opened_file.write(log_string + '\n') # 現(xiàn)在，發(fā)送一個(gè)通知 self.notify() return func(*args, **kwargs) return wrapped_function def notify(self): # logit只打日志，不做別的 pass @logit() def myfunc1(): pass
6.多層裝飾器的嵌套
#裝飾器1
def decorator1(func):
#定義裝飾之后的函數(shù)
def wrapper1():
# 裝飾器1
print('1-----裝飾1之前')
# 調(diào)用基本函數(shù)
func()
# 擴(kuò)展功能2
print('1-----裝飾1之后')
return wrapper1
#裝飾器2
def decorator2(func):
#定義裝飾之后的函數(shù)
def wrapper2():
# 裝飾器2
print('2-----裝飾2之前')
# 調(diào)用基本函數(shù)
func()
# 擴(kuò)展功能2
print('2-----裝飾2之后')
return wrapper2
#基本函數(shù)
@decorator2# 第二步：test = decorator2(eat) = test2
@decorator1# 第一步：test = decorator1(eat) = test1
def test():
print('測(cè)試')
#調(diào)用函數(shù)
test()
運(yùn)行結(jié)果：
2-----裝飾2之前
1-----裝飾1之前
測(cè)試
1-----裝飾1之后
2-----裝飾2之后Process finished with exit code 0
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