简单的装饰器函数：
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import time
from functools import wraps
def timethis(func):
"""
Decorator that reports the execution time.
"""
@wraps(func)
def wrapper(*args, **kwargs):
start = time.time()
result = func(*args, **kwargs)
end = time.time()
print(func.__name__, end-start)
return result
return wrapper
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函数的功能很简单，就是输出调用函数的执行时间。
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In [2]: @timethis
...: def countdown(n):
...: while n > 0:
...: n -= 1
...:
In [3]: countdown(100000)
countdown 0.009751319885253906
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本质上来说python的装饰器就是一个函数外再包装一个函数，等同于：
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timethis(countdown(100000))
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装饰器内部的wrapper()函数中使用*args和**kwargs来接受任意参数，并用新的函数包装器来代替原来函数，其中的func就是原来的函数，即调用包装器的函数。而使用@wraps(func)的目的时保留原始函数的元数据。
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In [19]: @timethis
...: def countdown(n:int):
...: '''counts down'''
...: while n > 0:
...: n -= 1
...:
In [20]: countdown(100000)
countdown 0.008384943008422852
In [21]: countdown.__name__
Out[21]: 'countdown'
In [22]: countdown.__doc__
Out[22]: 'counts down'
In [23]: countdown.__annotations__
Out[23]: {'n': int}
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输出的原始函数的元数据都正常
再来看看去掉wraps()函数的
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In [26]: countdown.__name__
Out[26]: 'wrapper'
In [27]: countdown.__doc__
In [28]: countdown.__annotations__
Out[28]: {}
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@wraps 有一个重要特征是它能让你通过属性 wrapped 直接访问被包装函数。例如:
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In [34]: countdown.__wrapped__.__name__
Out[34]: 'countdown'
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__wrapped__ 属性还能让被装饰函数正确暴露底层的参数签名信息。例如：
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In [43]: from inspect import signature
In [44]: signature(countdown)
Out[44]: <Signature (n:int)>
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带参数的装饰器
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import logging
from functools import wraps
def logged(level, name=None, message=None):
def decorate(func):
logname = name if name else func.__module__
log = logging.getLogger(logname)
logmsg = message if message else func.__name__
@wraps(func)
def wrapper(*args, **kwargs):
log.log(level, logmsg)
return func(*args, **kwargs)
return wrapper
return decorate
@logged(logging.DEBUG)
def add(x, y):
return x + y
@logged(logging.CRITICAL, 'example')
def spam():
print("Spam!")
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带可选参数的装饰器
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import logging
from functools import wraps, partial
def logged(func=None, *, level=logging.DEBUG, name=None, message=None):
if func is None:
return partial(logged, level=level, name=name, message=message)
logname = name if name else func.__module__
log = logging.getLogger(logname)
logmsg = message if message else func.__name__
@wraps(func)
def wrapper(*args, **kwargs):
log.log(level, logmsg)
return func(*args, **kwargs)
return wrapper
@logged
def add(x, y):
return x + y
@logged(level=logging.CRITICAL, name='example')
def spam():
print("Spam!")
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