Python中常见的装饰器（decorator）

本文将会介绍Python中几个工作中常见的装饰器。

本文将会介绍Python中几个日常工作中常用的装饰器（decorator），如下：

  • 计时装饰器
  • debug装饰器
  • 日志装饰器
  • 缓存装饰器
  • retry装饰器
  • 其它装饰器

计时装饰器

计时装饰器用于统计函数的运行时间，采用time模块，记录函数运行前、后时间，得到函数运行时间。示例Python代码如下：

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# -*- coding: utf-8 -*-
import time
from functools import wraps


def timer(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"Execution time of {func.__name__}: {end - start} seconds")
        return result
    return wrapper


@timer
def time_sleep(n):
    # sleep for n seconds
    time.sleep(n)
    return n


if __name__ == '__main__':
    t = time_sleep(3)
    print(t)

执行结果：

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Execution time of time_sleep: 3.0027120113372803 seconds
3

debug装饰器

debug装饰器用于代码debug，打印出运行函数的函数名及参数，用于debug。示例Python代码如下：

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# -*- coding: utf-8 -*-
from functools import wraps


def debug(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__} with args: {args} and kwargs: {kwargs}")
        result = func(*args, **kwargs)
        print(f"{func.__name__} returned: {result}")
        return result
    return wrapper


@debug
def greet(name, message="Hello"):
    """Returns a greeting message with the name"""
    return f"{message}, {name}!"


if __name__ == '__main__':
    print(greet("Alice"))
    print(greet("Bob", message="Hi"))

执行结果：

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Calling greet with args: ('Alice',) and kwargs: {}
greet returned: Hello, Alice!
Hello, Alice!
Calling greet with args: ('Bob',) and kwargs: {'message': 'Hi'}
greet returned: Hi, Bob!
Hi, Bob!

日志装饰器

日志装饰器用于在函数运行时打印日志，常用的日志模块有logging, loguru等。示例Python代码如下：

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# -*- coding: utf-8 -*-
from functools import wraps
import logging

logging.basicConfig(level=logging.DEBUG)
logger = logging.getLogger()


def log(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        args_repr = [repr(a) for a in args]
        kwargs_repr = [f"{k}={v!r}" for k, v in kwargs.items()]
        signature = ", ".join(args_repr + kwargs_repr)
        logger.debug(f"function {func.__name__} called with args {signature}")
        try:
            result = func(*args, **kwargs)
            return result
        except Exception as e:
            logger.exception(f"Exception raised in {func.__name__}. exception: {str(e)}")
            raise e
    return wrapper


@log
def divide(a, b, message='hi'):
    return a/b, message


if __name__ == '__main__':
    print(divide(2, 1, message='good'))
    print(divide(1, 0, message='bad'))

执行结果：

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DEBUG:root:function divide called with args 2, 1, message='good'
DEBUG:root:function divide called with args 1, 0, message='bad'
ERROR:root:Exception raised in divide. exception: division by zero
Traceback (most recent call last):
  File "/Users/admin/PycharmProjects/env_test/custom_decorator/log_decorator.py", line 17, in wrapper
    result = func(*args, **kwargs)
  File "/Users/admin/PycharmProjects/env_test/custom_decorator/log_decorator.py", line 27, in divide
    return a/b, message
ZeroDivisionError: division by zero
Traceback (most recent call last):
  File "/Users/admin/PycharmProjects/env_test/custom_decorator/log_decorator.py", line 32, in <module>
    print(divide(1, 0, message='bad'))
  File "/Users/admin/PycharmProjects/env_test/custom_decorator/log_decorator.py", line 21, in wrapper
    raise e
  File "/Users/admin/PycharmProjects/env_test/custom_decorator/log_decorator.py", line 17, in wrapper
    result = func(*args, **kwargs)
  File "/Users/admin/PycharmProjects/env_test/custom_decorator/log_decorator.py", line 27, in divide
    return a/b, message
ZeroDivisionError: division by zero
(2.0, 'good')

缓存装饰器

缓存装饰器用于实现缓存，比如LRU Cache等。下面的例子将使用LRU Cache来缓存fibonacci函数的中间运行结果，从而加快函数运行时间，代码如下：

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# -*- coding: utf-8 -*-
import time
from functools import lru_cache


def fibonacci(n):
    if n <= 1:
        return 1
    else:
        return fibonacci(n-1) + fibonacci(n-2)


@lru_cache(maxsize=5)
def cache_fibonacci(n):
    if n <= 1:
        return 1
    else:
        return cache_fibonacci(n-1) + cache_fibonacci(n-2)


if __name__ == '__main__':
    t1 = time.time()
    print(fibonacci(37))
    t2 = time.time()
    print(t2 - t1)
    print(cache_fibonacci(37))
    print(time.time() - t2)

执行结果：

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39088169
3.7291252613067627
39088169
4.291534423828125e-05

retry装饰器

在工程项目中，尝尝会遇到数据库连接、HTTP连接等，这时一般都会加个retry（重连）机制，用于连接中断时发起重新连接，避免不必要的错误。Python中常见的retry模块有retry, tenacity等。

下面的示例代码将演示在断网情况下的HTTP重连：

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# -*- coding: utf-8 -*-
import requests
from retry import retry
import logging

logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s  %(filename)s : %(levelname)s  %(message)s')
logger = logging.getLogger()


@retry(exceptions=Exception, tries=5, delay=1, backoff=2, max_delay=30, logger=logger)
def make_requests():
    url = "https://www.example.com/"
    response = requests.get(url)
    return response.content


if __name__ == '__main__':
    print(make_requests())

执行结果：

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2023-12-18 13:09:28,869  connectionpool.py : DEBUG  Starting new HTTPS connection (1): www.example.com:443
2023-12-18 13:09:28,870  api.py : WARNING  HTTPSConnectionPool(host='www.example.com', port=443): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x103959e10>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')), retrying in 1 seconds...
2023-12-18 13:09:29,872  connectionpool.py : DEBUG  Starting new HTTPS connection (1): www.example.com:443
2023-12-18 13:09:29,872  api.py : WARNING  HTTPSConnectionPool(host='www.example.com', port=443): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x1039590f0>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')), retrying in 2 seconds...
2023-12-18 13:09:31,874  connectionpool.py : DEBUG  Starting new HTTPS connection (1): www.example.com:443
2023-12-18 13:09:31,875  api.py : WARNING  HTTPSConnectionPool(host='www.example.com', port=443): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x103959210>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')), retrying in 4 seconds...
2023-12-18 13:09:35,878  connectionpool.py : DEBUG  Starting new HTTPS connection (1): www.example.com:443
2023-12-18 13:09:35,878  api.py : WARNING  HTTPSConnectionPool(host='www.example.com', port=443): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x103959510>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')), retrying in 8 seconds...
2023-12-18 13:09:43,882  connectionpool.py : DEBUG  Starting new HTTPS connection (1): www.example.com:443

其它装饰器

Python中还有许许多多的装饰器，使用装饰器不仅能使我们的代码简洁美观，而且非常方便实用，比如在Torch中，可以使用@torch.no_grad()装饰器来代替torch.no_grad()写法，非常方便，如下：

torch.no_grad() 的装饰器使用方法：

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@torch.no_grad()
def eval():
	...

总结

在Python中，装饰器是十分常见且好用的功能，实现起来也不困难，后续有机会讲仔细讲解装饰器的原理及其实现。

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Python
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Python中常见的装饰器（decorator）
https://percent4.github.io/Python中常见的装饰器（decorator）/
作者
Jclian91
发布于
2024年1月11日
许可协议