python - 如何处理代理类中的不可用主机(ConnectionRefusedError)

Question

我有一个非常基本的代理类(一个帮我编码的 friend 坚称它是一个装饰器类)python-mpd2 .

类看起来是这样的

import mpd

class MPDProxy:
    def __init__(self, host="localhost", port=6600, timeout=10):
        self.client = mpd.MPDClient()
        self.host = host
        self.port = port

        self.client.timeout = timeout
        self.connect(host, port)

    def __getattr__(self, name):
        return self._call_with_reconnect(getattr(self.client, name))

    def connect(self, host, port):
        self.client.connect(host, port)

    def _call_with_reconnect(self, func):
        def wrapper(*args, **kwargs):
            try:
                return func(*args, **kwargs)
            except mpd.ConnectionError:
                self.connect(self.host, self.port)
                return func(*args, **kwargs)
        return wrapper

mpd_proxy = MPDProxy()

到目前为止，只要有可连接的 mpd 主机，它就可以正常工作。如果没有 mpd 服务器，我得到

ConnectionRefusedError: [Errno 111] Connection refused

我正在寻找好的模式来处理这个异常

• 你能想出一种优雅的方法来防止程序在没有可用主机时崩溃吗？
• 无论何时调用代理，我应该在代理内部还是外部捕获异常？
• 将字符串“Host not available”(或类似的)作为返回值是个好主意，还是可以以更好的方式通知调用代理的方法/函数？

Answer 1

Can you think of an elegant way to prevent the program to crash, when there is no host available?

尝试...除了 ;)

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Should I catch the exception within the proxy or outside, whenever the proxy is called?

您应该问自己的问题是“谁*能够*处理该异常？”

显然，代理无法对“修复”ConnectionRefusedError 进行任何明智的处理。所以它必须在上层处理。

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Is a string "Host not available" (or similar) as a return value a good idea or can a method/function calling the proxy be informed in a better way?

坏主意。通知“上层”异常发生的正常方法是引发异常。或者让引发的异常向上传播。

---

具体来说:

class MPDProxy:
    def _call_with_reconnect(self, func):
        def wrapper(*args, **kwargs):
            try:
                return func(*args, **kwargs)
            except mpd.ConnectionError:
                self.connect(self.host, self.port)
                # ^^^^^^ This lime might raise `ConnectionRefusedError`
                # as there is no `except` block around, this exception
                # is automatically propagated     

                return func(*args, **kwargs)
        return wrapper

try:
    mpd_proxy = MPDProxy()
    r = mdp_proxy._call_with_reconnect(whatever)
except ConnectionRefusedError:
    do_somesible_sensible()