装饰器小酌

python

Python中的装饰器真是个好东西。熟悉我的人都知道，挺能喷的一个人。但是，技术不是喷出来的，前言写的再花，也不会让我的装饰器比别人的更有威力。哈哈哈

开撸

装饰器是 Python 提供的一个语法糖，即：一个函数接受另一个函数作为参数并返回一个新的函数

func = decorate(func)

不带参数的

In [17]: from functools import wraps
    ...: 
    ...: def log(func):
    ...:     @wraps(func)
    ...:     def wrapper(*args, **kw):
    ...:         print("I'm a log ^*^")
    ...:         result = func(*args, **kw)
    ...:         return result
    ...:     return wrapper
    ...: 
In [19]: @log
    ...: def hello():
    ...:     print('Hello World')
    ...:     
In [20]: hello()
I'm a log ^*^
Hello World

带参数的怎么写呢？？？

请看

In [5]: from functools import wraps
In [8]: def logs(file="info.log"):
   ...:     def decorate(func):
   ...:         @wraps(func)
   ...:         def wrapper(*args, **kw):
   ...:             log = func.__name__ + " was called"
   ...:             print(log)
   ...:             with open(file, 'a') as f:
   ...:                 f.write(log + '\n')
   ...:         return wrapper
   ...:     return decorate
   ...: 
In [11]: @logs()
    ...: def hello():
    ...:     print('Hello World!')
    ...:     
In [12]: hello()
hello was called
In [13]: @logs(file='info2.log')
    ...: def hello2():
    ...:     print('Hello World!')
    ...:     
In [14]: hello2()
hello2 was called

带参数和不带参数

from functools import wraps, partial
import logging
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
# Example use
@logged
def add(x, y):
    return x + y
@logged(level=logging.CRITICAL, name='example') # 高于 warning 级别的才会输出到屏幕
def spam():
    print('Spam!')

就到这里吧，反正很少有人会来看。就一个人浪吧。

更新

类装饰器

In [1]: class Log():
   ...:     def __init__(self, file="info.log"):
   ...:         self.file = file
   ...:     def __call__(self, func):
   ...:         log = func.__name__  + " was called"
   ...:         print(log)
   ...:         with open(self.file, 'a') as f:
   ...:             f.write(log+'\n')
   ...: 
In [2]: @Log()
   ...: def hello():
   ...:     print('Hello World!')
   ...:     
hello was called

可复制粘贴代码在这里

缓存

# coding: utf-8
import functools
def cache(func):
    _cache = {}
    functools.wraps(func)
    def wrapper(*args):
        result = _cache.get(args)
        if not result:
            result = func(*args)
            _cache[args] = result
        return result
    return wrapper
# test
In [5]: @cache
   ...: def fib(n):
   ...:     if n < 2:
   ...:         return n
   ...:     return fib(n-1) + fib(n-2)
   ...: 
In [6]: %time fib(200)
CPU times: user 0 ns, sys: 0 ns, total: 0 ns
Wall time: 723 µs   
Out[6]: 280571172992510140037611932413038677189525
In [7]: %time fib(200)
CPU times: user 0 ns, sys: 0 ns, total: 0 ns
Wall time: 11.2 µs     # 时间大幅减少
Out[7]: 280571172992510140037611932413038677189525
In [8]: %time fib(200)
CPU times: user 0 ns, sys: 0 ns, total: 0 ns
Wall time: 13.4 µs
Out[8]: 280571172992510140037611932413038677189525

flask_login.login_required

flask_login.login_required 是也是一个装饰器，login_required 装饰器的主要作用就是让只有已登陆和认证过的用户才能继续调用被其装饰的视图(view)函数。下面是截取的 片段

def login_required(func):
    @wraps(func)
    def decorated_view(*args, **kwargs):
        if request.method in EXEMPT_METHODS:
            return func(*args, **kwargs)
        elif current_app.login_manager._login_disabled:
            return func(*args, **kwargs)
        elif not current_user.is_authenticated:
            return current_app.login_manager.unauthorized()
        return func(*args, **kwargs)
    return decorated_view

参考

1. 哦，对了，附上一个牛逼的链接，墙裂推荐不熟悉装饰器的小伙伴们看看。

2. Python tips Decorates

3. Python CookBook