python 装饰器之应用示例

import time
import hashlib
import pickle
import threading

#装饰函数缓存应用

cache ={}

def is_obsolete(entry,duration):
    return time.time() - entry['time']>duration

def compute_key(function,args,kw):
    key = pickle.dumps((function.__name__,args,kw))
    return hashlib.sha1(key).hexdigest()

def momoize(duration=10):
    def __momoize(function):
        def __momoize(*args,**kw):
            key = compute_key(function,args,kw)
            #是否已经拥有了它？
            if(key in cache and not is_obsolete(cache[key],duration)):
                print('we got a winner')
                return cache[key]['value']
            #计算
            result =function(*args,**kw)
            #保存结果
            cache[key] ={
                'value':result,
                'time':time.time()
            }
            return result
        return __momoize
    return __momoize

@momoize(5)
def very_very_complex_stuff(a,b):
    #如果在执行计算时计算机过热
    #请终止程序
    return a + b

# very_very_complex_stuff(1,1)
# very_very_complex_stuff(2,2)
# very_very_complex_stuff(3,3)
# very_very_complex_stuff(4,4)
# print(cache)
# time.sleep(5)
# very_very_complex_stuff(1,1)
# very_very_complex_stuff(2,2)
# very_very_complex_stuff(3,3)
# very_very_complex_stuff(4,4)
# print(cache)

#代理

class User(object):
    def __init__(self,roles):
        self.roles =roles

class Unauthorized(Exception):
    pass

def protect(role):
    def _protect(function):
        def __protect(*args,**kw):
            user = globals().get('user')
            if(user is None or role not in user.roles):
                raise Unauthorized("I wo'nt tell you")
            return function(*args,**kw)
        return __protect
    return _protect

tarek =User(('admin','user'))
bill =User(('user'))

class Mysecrets(object):
    @protect('admin')
    def waffle_recipe(self):
        print('user tons of butter!')

# these_are = Mysecrets()
# user = tarek
# these_are.waffle_recipe()

#上下文

from threading import RLock
lock =RLock()

def synchronized(function):
    def _synchronized(*args,**kw):
        lock.acquire()
        try:
            return function(*args,**kw)
        finally:
            lock.release()
        return _synchronized

@synchronized
def thread_safe():
    pass

class ContextIllustration:
    def __enter__(self):
        print('entering context')

    def __exit__(self,exc_type,exc_value,traceback):
        print('leaving context')

        if exc_type is None:
            print('with no error')
        else:
            print('with an error (%s)'%exc_value)

# with ContextIllustration():
#      print('inside')

from contextlib import contextmanager

@contextmanager
def contextillustration():
    print('entering context')
    try:
        yield
    except Exception as e:
        print('leaving context')
        print('with an error (%s)'%e)
        raise
    else:
        print('leaving context')
        print('with no error')          

with contextillustration():
    print('inside')

for number in range(1):
    break
else:
   print('no break')