python - 多态异常处理: How to catch subclass exception?

我有以下两个C++异常的简单层次结构:

class LIB_EXP ClusterException : public std::exception {
public:
    ClusterException() { }
    ClusterException(const std::string& what) { init(what); }
    virtual const char* what() const throw() { return what_.c_str(); }
    virtual ~ClusterException() throw() {}
    virtual ClusterException* clone() { return new ClusterException(*this);  }
protected:
    void init(const std::string& what) { what_ = what; }
private:
    std::string what_;
};

class LIB_EXP ClusterExecutionException : public ClusterException {
public:
    ClusterExecutionException(const std::string& jsonResponse);
    std::string getErrorType() const throw() { return errorType_; }
    std::string getClusterResponse() const throw() { return clusterResponse_; }
    virtual ~ClusterExecutionException() throw() {}
    virtual ClusterExecutionException* clone() { return new ClusterExecutionException(*this);  }
private:
    std::string errorType_;
    std::string clusterResponse_;
};

然后，我按如下所示将它们导出到带有Boost-Python的Python中。请注意我对bases的使用，以确保在翻译中保留继承关系:

class_<ClusterException> clusterException("ClusterException", no_init);
clusterException.add_property("message", &ClusterException::what);
clusterExceptionType = clusterException.ptr();
register_exception_translator<ClusterException>(&translateClusterException);

class_<ClusterExecutionException, bases<ClusterException> > clusterExecutionException("ClusterExecutionException", no_init);
clusterExecutionException.add_property("message", &ClusterExecutionException::what)
                         .add_property("errorType", &ClusterExecutionException::getErrorType)
                         .add_property("clusterResponse", &ClusterExecutionException::getClusterResponse);
clusterExecutionExceptionType = clusterExecutionException.ptr();
register_exception_translator<ClusterExecutionException>(&translateClusterExecutionException);

然后是异常翻译方法:

static PyObject *clusterExceptionType = NULL;
static void translateClusterException(ClusterException const &exception) {
  assert(clusterExceptionType != NULL);
  boost::python::object pythonExceptionInstance(exception);
  PyErr_SetObject(clusterExceptionType, pythonExceptionInstance.ptr());
}

static PyObject *clusterExecutionExceptionType = NULL;
static void translateClusterExecutionException(ClusterExecutionException const &exception) {
  assert(clusterExecutionExceptionType != NULL);
  boost::python::object pythonExceptionInstance(exception);
  PyErr_SetObject(clusterExecutionExceptionType, pythonExceptionInstance.ptr());
}

我创建了以下抛出异常的测试C++函数:

static void boomTest(int exCase) {
  switch (exCase) {
    case 0:  throw ClusterException("Connection to server failed");
             break;
    case 1:  throw ClusterExecutionException("Error X while executing in the cluster");
             break;
    default: throw std::runtime_error("Unknown exception type");
  }
}

最后，调用我的C++ boomTest的Python测试代码:

import cluster
reload(cluster)
from cluster import ClusterException, ClusterExecutionException

def test_exception(exCase):
    try:
        cluster.boomTest(exCase)

    except ClusterException as ex:
        print 'Success! ClusterException gracefully handled:' \
            '\n message="%s"' % ex.message
    except ClusterExecutionException as ex:
        print 'Success! ClusterExecutionException gracefully handled:' \
            '\n message="%s"' \
            '\n errorType="%s"' \
            '\n clusterResponse="%s"' % (ex.message, ex.errorType, ex.clusterResponse)
    except:
        print 'Caught unknown exception: %s "%s"' % (sys.exc_info()[0], sys.exc_info()[1])

def main():
    print '\n************************ throwing ClusterException ***********************************************************************'
    test_exception(0)
    print '\n************************ throwing ClusterExecutionException **************************************************************'
    test_exception(1)
    print '\n************************ throwing std::runtime_error *********************************************************************'
    test_exception(2)

if __name__ == "__main__":
    main()

到这里为止一切正常。但是，如果我从Python中删除ClusterExecutionException捕获处理程序，则将捕获此异常并将其回退到未知异常，而不是作为其基本ClusterException捕获。

我在Boost-Python中尝试过，将ClusterExecutionException的异常转换注册为基本ClusterException时，将其“多态”地捕获，但不会被捕获为ClusterExecutionException。如何使ClusterExecutionException同时被捕获为ClusterException和ClusterExecutionException？我尝试过将ClusterExecutionException异常同时注册为ClusterException和ClusterExecutionException，但是它遵循了最后的获胜策略，只有一个不能同时使用。

还有其他解决方法吗？

更新1:这个问题的致命一面是在C++方面找出except Python语句的类型，例如except ClusterException as ex:，一旦在C++端内部就未知。 Boost.Python进行的异常转换将调用与异常的动态类型相对应的转换函数，而Python catch静态类型未知。

更新2:如建议将Python代码更改为以下代码，即添加print(type(ex).__bases__)可以得到:

def test_exception(exCase):
    try:
        cluster.boomTest(exCase)

    except ClusterException as ex:
        print(type(ex).__bases__)
        print 'Success! ClusterException gracefully handled:' \
            '\n message="%s"' % ex.message
    except ClusterExecutionException as ex:
        print(type(ex).__bases__)
        print 'Success! ClusterExecutionException gracefully handled:' \
            '\n message="%s"' \
            '\n errorType="%s"' \
            '\n clusterResponse="%s"' % (ex.message, ex.errorType, ex.clusterResponse)
    except:
        print 'Caught unknown exception: %s "%s"' % (sys.exc_info()[0], sys.exc_info()[1])

和输出:

************************ throwing ClusterException ***********************************************************************
(<type 'Boost.Python.instance'>,)
Success! ClusterException gracefully handled:
 message="Connection to server failed"

************************ throwing ClusterExecutionException **************************************************************
(<class 'cluster.ClusterException'>,)
Success! ClusterExecutionException gracefully handled:
 message="Error X while executing in the cluster"
 errorType="LifeCycleException"
 clusterResponse="{ "resultStatus": "Error", "errorType": "LifeCycleException", "errorMessage": "Error X while executing in the cluster" }"

这意味着继承关系是从Python中“看到的”。但是多态处理仍然不起作用。

更新3 这是运行VS dumpbin.exe的输出:

我使用的命令是:

dumpbin.exe /EXPORTS /SYMBOLS C:\ClusterDK\x64\Debug\ClusterDK.dll > c:\temp\dumpbin.out

以及输出的相关部分:

Microsoft (R) COFF/PE Dumper Version 11.00.50727.1
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file C:\ClusterDK\x64\Debug\ClusterDK.dll

File Type: DLL

Section contains the following exports for ClusterDK.dll

00000000 characteristics
5A1689DA time date stamp Thu Nov 23 09:42:02 2017
    0.00 version
       1 ordinal base
      78 number of functions
      78 number of names

ordinal hint RVA      name

      8    7 00004485 ??0ClusterException@cluster@@QEAA@AEBV01@@Z = @ILT+13440(??0ClusterException@cluster@@QEAA@AEBV01@@Z)
      9    8 00001659 ??0ClusterException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z = @ILT+1620(??0ClusterException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z)
     10    9 00001F1E ??0ClusterException@cluster@@QEAA@XZ = @ILT+3865(??0ClusterException@cluster@@QEAA@XZ)
     11    A 00004D4F ??0ClusterExecutionException@cluster@@QEAA@AEBV01@@Z = @ILT+15690(??0ClusterExecutionException@cluster@@QEAA@AEBV01@@Z)
     12    B 000010AA ??0ClusterExecutionException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z = @ILT+165(??0ClusterExecutionException@cluster@@QEAA@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z)
     27   1A 000035D0 ??1ClusterException@cluster@@UEAA@XZ = @ILT+9675(??1ClusterException@cluster@@UEAA@XZ)
     28   1B 00003C7E ??1ClusterExecutionException@cluster@@UEAA@XZ = @ILT+11385(??1ClusterExecutionException@cluster@@UEAA@XZ)
     37   24 00002BD5 ??4ClusterException@cluster@@QEAAAEAV01@AEBV01@@Z = @ILT+7120(??4ClusterException@cluster@@QEAAAEAV01@AEBV01@@Z)
     38   25 000034D1 ??4ClusterExecutionException@cluster@@QEAAAEAV01@AEBV01@@Z = @ILT+9420(??4ClusterExecutionException@cluster@@QEAAAEAV01@AEBV01@@Z)
     46   2D 000D2220 ??_7ClusterException@cluster@@6B@ = ??_7ClusterException@cluster@@6B@ (const cluster::ClusterException::`vftable')
     47   2E 000D2248 ??_7ClusterExecutionException@cluster@@6B@ = ??_7ClusterExecutionException@cluster@@6B@ (const cluster::ClusterExecutionException::`vftable')
     52   33 00004BB5 ?clone@ClusterException@cluster@@UEAAPEAV12@XZ = @ILT+15280(?clone@ClusterException@cluster@@UEAAPEAV12@XZ)
     53   34 00004D31 ?clone@ClusterExecutionException@cluster@@UEAAPEAV12@XZ = @ILT+15660(?clone@ClusterExecutionException@cluster@@UEAAPEAV12@XZ)
     61   3C 00001D43 ?getErrorType@ClusterExecutionException@cluster@@QEBA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ = @ILT+3390(?getErrorType@ClusterExecutionException@cluster@@QEBA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ)
     69   44 0000480E ?init@ClusterException@cluster@@IEAAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z = @ILT+14345(?init@ClusterException@cluster@@IEAAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z)
     78   4D 000032FB ?what@ClusterException@cluster@@UEBAPEBDXZ = @ILT+8950(?what@ClusterException@cluster@@UEBAPEBDXZ)

Summary

    4000 .data
    5000 .idata
   12000 .pdata
   54000 .rdata
    2000 .reloc
    1000 .rsrc
   C9000 .text
    1000 .tls

最佳答案

我的python技能很生疏，我还没有测试过，所以这可能需要进一步的改进，但是请尝试添加异常转换方法来处理基类异常类型:

static PyObject *clusterExecutionAsClusterExceptionType = NULL;
static void translateClusterExecutionAsClusterException(ClusterException const &exception) {

  ClusterExecutionException* upcasted = dynamic_cast<ClusterExecutionException*>(&exception);
  if (upcasted)
  {
    assert(clusterExecutionAsClusterExceptionType != NULL);
    boost::python::object pythonExceptionInstance(*upcasted);
  PyErr_SetObject(clusterExecutionAsClusterExceptionType, pythonExceptionInstance.ptr());
  }
}

register_exception_translator<ClusterException>(&translateClusterExecutionAsClusterException);

关于python - 多态异常处理: How to catch subclass exception?，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/46420476/