如何尝试一些东西，如果失败了，尝试其他的东西？

Question

我正在写一个脚本，我需要尝试在一封电子邮件上应用几种解析方法。因此，如果第一个成功了，就没有必要尝试其他的了。到目前为止，我只有2个解析方法，但我可能会添加更多。如果可能的话，我想复制一些类似switch case的东西(在2.7中不存在)。有没有比我现在做的更好的？

try:
    found['PhishMe_Informations']=self.parse_phishme(message)

except MalformedPhishMeMailError as e:
    self.log.error(e[0])
    found['PhishMe_Informations']=e[1]
    found['PhishMe_Informations']['Malformed']=True

except Exception:
    try:
        found['Journaling_Informations']=self.parse_journaling(message)

    except MalformedRecordMessageError as e:
         self.log.error(e)

    except Exception:
        pass

Answer 1

您可以尝试以声明模式构建函数和可能的异常的分层树，然后编写处理它的代码。在您的用例中，它可能是：

{ cls.parse_phishme: OrderedDict(
        (MalformedPhishMeMailError, cls.process_malformed),
        (Exception, { cls.parse_journaling: OrderedDict(
                (MalformedRecordMessageError, cls.log_err),
                (Exception, None)
            )
    )
}

处理该树的方法可以是：

def process_exc_tree(self, d, message):
    if isinstance(d, dict):   # is d a (possibly ordered) dict?
        for func, exc in d.items():
            try:
                self.func(message)    # call the function passed as key
            except Exception as e:              # process the exceptions
                for ex, suite in exc.items():   #  passed as ordered dict
                    if isinstance(e, ex):
                        # Ok found the relevant exception: recurse
                        self.process_exc_tree(suite, message)
    elif d is None:           # if d is None, do nothing
        pass
    else:                     # it should be a function: call it
        self.d(message)