Python中的裝飾器
不帶參數(shù)的裝飾器
#!coding:utf-8
def use_logging(func):
def wrapper(*args, **kwargs):
print("%s is running" % func.__name__)
return func(*args)
return wrapper
@use_logging
def foo():
print("i am foo")
@use_logging
def bar():
print("i am bar")
foo()
bar()
帶參數(shù)的裝飾器
#!coding:utf-8
def use_logging(level):
def decorator(func):
def wrapper(*args, **kwargs):
print("[%s]%s is running" % (level, func.__name__))
return func(*args)
return wrapper
return decorator
@use_logging(level='error')
def foo():
print("i am foo")
@use_logging(level='warn')
def bar():
print("i am bar")
foo()
bar()
類裝飾器
#!coding:utf-8
class Foo(object):
def __init__(self, func):
self._func = func
def __call__(self):
print('class decorator runing')
self._func()
print('class decorator ending')
@Foo
def bar():
print('bar')
bar()
functools.wraps
使用裝飾器極大地復(fù)用了代碼撒踪，但是他有一個(gè)缺點(diǎn)就是原函數(shù)的元信息不見了愉豺，比如函數(shù)的 docstring、__name__、參數(shù)列表，先看例子：
#!coding:utf-8
def logged(func):
def with_logging(*args, **kwargs):
print(func.__name__ + " was called")
return func(*args, **kwargs)
return with_logging
@logged
def f(x):
"""does some math"""
return x + x * x
print(f.__name__) # prints 'with_logging'
print(f.__doc__) # prints None
函數(shù) f 等價(jià)于：
def f(x):
"""does some math"""
return x + x * x
f = logged(f)
不難發(fā)現(xiàn)箕肃，函數(shù) f 被 with_logging 取代了，當(dāng)然它的 docstring最盅，__name__ 就是變成了with_logging函數(shù)的信息了突雪。
這個(gè)問題就比較嚴(yán)重的，好在我們有 functools.wraps涡贱，wraps 本身也是一個(gè)裝飾器咏删，它能把原函數(shù)的元信息拷貝到裝飾器函數(shù)中，這使得裝飾器函數(shù)也有和原函數(shù)一樣的元信息了问词。
from functools import wraps
def logged(func):
@wraps(func)
def with_logging(*args, **kwargs):
print(func.__name__ + " was called")
return func(*args, **kwargs)
return with_logging
@logged
def f(x):
"""does some math"""
return x + x * x
print(f.__name__) # prints 'f'
print(f.__doc__) # prints 'does some math'
內(nèi)置裝飾器
@staticmathod督函、@classmethod、@property
裝飾器的順序
@a
@b
@c
def f ():
等效于
f = a(b(c(f)))