提示

装饰器主要应用场景：包括插入日志、性能测试、事务处理、缓存和权限验证。

在执行某个函数前后，要进行特俗的处理，并且大量的地方需要使用的时候，可以把该逻辑封装为装饰器。

带参装饰器

#!/usr/bin/env python
# coding=utf-8
import logging
import time
from functools import wraps


def retry(exception, tries=3, delay=1, back_off=1, logger=None):
    """Retry calling the decorated function using an exponential backoff.

    http://www.saltycrane.com/blog/2009/11/trying-out-retry-decorator-python/
    original from: http://wiki.python.org/moin/PythonDecoratorLibrary#Retry

    :param exception: the exception to check. may be a tuple of
        exceptions to check
    :type exception Exception
    :param tries: number of times to try (not retry) before giving up
    :type tries: int
    :param delay: initial delay between retries in seconds
    :type delay: int
    :param back_off: back off multiplier e.g. value of 2 will double the delay
        each retry
    :type back_off: int
    :param logger: logger to use. If None, print
    :type logger: logging.Logger instance
    """

    def deco_retry(f):
        @wraps(f)
        def f_retry(*args, **kwargs):
            count = 0
            cause = ""
            m_tries, m_delay = tries, delay
            event_name = args[1]
            while m_tries > 1:
                try:
                    count += 1
                    return f(*args, **kwargs)
                except exception as e:
                    cause = e
                    msg = "%s report failed, try again %s times, %s" % (event_name, count, e)
                    if logger:
                        logging.warning(msg)
                    if m_delay > 0:
                        time.sleep(1)
                    m_tries -= 1
                    m_delay *= back_off
            logging.error("%s push failed: %s", event_name, cause)
            return False, True

        return f_retry  # true decorator

    return deco_retry



@retry(2)
def hello():
    """doc"""
    print('hello')


hello()
# 注意加了和不加 @wraps(func) 下面打印的结果
print(hello.__doc__)
print(hello.__name__)

不带参装饰器

def log(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        """打印函数的返回结果"""
        res = func(*args, **kwargs)
        print('函数{}返回的结果为：{}'.format(func.__name__, res))
        return res

    return wrapper


@log
def demo(num1, num2):
    return num1 + num2


@log
def demo1():
    return 'hello world!'


demo(1, 2)
demo1()

案例

# 登录验证，调用每个接口都会校验是否已登录
token = ''


def login(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        """模拟验证是否登录"""
        if not token:  # 这个token一般是存在数据库(redis/mysql等)的，这里在代码里面模拟写死了
            return '没有登录，请登录后使用'
        return func(*args, **kwargs)

    return wrapper


@login
def post1():
    """模拟一个post请求，调用该请求会先去检查是否登录"""
    pass


@login
def post2():
    """模拟一个post请求，调用该请求会先去检查是否登录"""
    pass


print(post1())
print(post2())