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我终于弄懂了Python的装饰器

装饰器应该在何时发挥作用?
现在有个大问题:
我可以使用装饰器做什么?

装饰器看起来很酷而且功能强大,但是展示一个实际的例子会更清晰。
使用的场景有1000种可能性。但是经典用法:

通过外部库来扩展函数的行为(在您不能对其进行修改的情况下)。
用于调试(您不希望对其进行修改,因为它是临时的)。
重复使用功能,可以通过装饰器来加到其他多个函数上。
您可以使用它们以链式的方式扩展多个功能,如下所示:

def benchmark(func):
“””
装饰器,打印函数执行花费的时间。
“””
import time
def wrapper(*args, **kwargs):
t = time.clock()
res = func(*args, **kwargs)
print(“{0} {1}”.format(func.__name__, time.clock()-t))
return res
return wrapper

def logging(func):
“””
装饰器,记录脚本的活动。(它实际上只是打印出来,但可能是在记录日志!)
“””
def wrapper(*args, **kwargs):
res = func(*args, **kwargs)
print(“{0} {1} {2}”.format(func.__name__, args, kwargs))
return res
return wrapper

def counter(func):
“””
装饰器,计算并打印执行功能的次数
“””
def wrapper(*args, **kwargs):
wrapper.count = wrapper.count + 1
res = func(*args, **kwargs)
print(“{0} has been used: {1}x”.format(func.__name__, wrapper.count))
return res
wrapper.count = 0
return wrapper

@counter
@benchmark
@logging
def reverse_string(string):
return str(reversed(string))

print(reverse_string(“Able was I ere I saw Elba”))
print(reverse_string(“A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal: Panama!”))

#输出:
#reverse_string (‘Able was I ere I saw Elba’,) {}
#wrapper 0.0
#wrapper has been used: 1x
#ablE was I ere I saw elbA
#reverse_string (‘A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal: Panama!’,) {}
#wrapper 0.0
#wrapper has been used: 2x
#!amanaP :lanac a ,noep a ,stah eros ,raj a ,hsac ,oloR a ,tur a ,mapS ,snip ,eperc a ,)lemac a ro( niaga gab ananab a ,gat a ,nat a ,gab ananab a ,gag a ,inoracam ,elacrep ,epins ,spam ,arutaroloc a ,shajar ,soreh ,atsap ,eonac a ,nalp a ,nam A
当然,使用装饰器的好处是您可以立即在几乎所有内容上使用它们而无需重写。比如:

@counter
@benchmark
@logging
def get_random_futurama_quote():
from urllib import urlopen
result = urlopen(“http://subfusion.net/cgi-bin/quote.pl?quote=futurama”).read()
try:
value = result.split(“<br><b><hr><br>”)[1].split(“<br><br><hr>”)[0]
return value.strip()
except:
return “No, I’m … doesn’t!”

print(get_random_futurama_quote())
print(get_random_futurama_quote())

#输出:
#get_random_futurama_quote () {}
#wrapper 0.02
#wrapper has been used: 1x
#The laws of science be a harsh mistress.
#get_random_futurama_quote () {}
#wrapper 0.01
#wrapper has been used: 2x
#Curse you, merciful Poseidon!

 

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