Try-Except-Else-Finally return in else Alternative？

Question

我正在开发一个可以raise 多个Exceptions 的函数。我想在它们的 except 块中处理这些Exceptions，然后返回带有自定义消息和回溯的结果。问题是finally 是有保证的，所以我不能在else 块内返回任何东西。

如果引发了一些Exception，则此代码有效，但如果没有Exception，则此代码无效。在这种情况下，我只想返回{'success':True}。

所以从这段代码：

def foo():
    try:
        #some code
        return {'success':True}
    except FirstException:
        tb = traceback.format_exc()
        msg = 'There was FirstExc'
        return {'success':False,
                'tb':tb,
                'msg':msg}
    except SecondException:
        tb = traceback.format_exc()
        msg = 'There was SecondExc'
        return {'success':False,
                'tb':tb,
                'msg':msg}
    ...

我不想重复returns。我试过了：

def foo():
    try:
        pass
    except FirstException:
        tb = traceback.format_exc()
        msg = 'There was FirstExc'
    except SecondException:
        tb = traceback.format_exc()
        msg = 'There was SecondExc'
    else:
        return {'success':True}
    finally:
        return {'success':False,
                'tb':tb,
                'msg':msg}

你知道怎么做吗？我知道我可以将return {'success':True} 放入try 块中，删除finally 和else 块并将return {'success':False,'tb':tb,'msg':msg} 添加到每个except 块中，但是有很多except 块，因此代码会重复多次.

还有其他选择吗？

Answer 1

不要使用finally 块。您只想为异常返回False，否则返回True；返回finally 始终适用于这两种情况。

您可以从两个except 套房返回，也可以合并这两个套房。

从两者返回会导致更多重复：

def foo():
    try:
        pass
    except FirstException:
        tb = traceback.format_exc()
        msg = 'There was FirstExc'
        return {'success':False,
                'tb':tb,
                'msg':msg}
    except SecondException:
        tb = traceback.format_exc()
        msg = 'There was SecondExc'
        return {'success':False,
                'tb':tb,
                'msg':msg}
    else:
        return {'success':True}

您可以将except 套件合二为一：

def foo():
    try:
        pass
    except (FirstException, SecondException) as e:
        tb = traceback.format_exc()
        exception_type = 'FirstExc' if isinstance(e, FirstException) else 'SecondExc'
        msg = 'There was {}'.format(exception_type)
        return {'success':False,
                'tb':tb,
                'msg':msg}
    else:
        return {'success':True}

另一种选择是先构建返回值，然后根据需要添加信息：

def foo():
    result = {'success': True}
    try:
        pass
    except FirstException:
        tb = traceback.format_exc()
        msg = 'There was FirstExc'
        result = {'success': False, 'tb': tb, 'msg': msg}
    except SecondException:
        tb = traceback.format_exc()
        msg = 'There was SecondExc'
        result = {'success': False, 'tb': tb, 'msg': msg}
    finally:
        return result

不过，这与 return-from-the-except-suite 选项并没有什么不同。

Answer 2

def foo():
    success = False
    try:
        pass
    except FirstException:
        tb = traceback.format_exc()
        msg = 'There was FirstExc'
    except SecondException:
        tb = traceback.format_exc()
        msg = 'There was SecondExc'
    else:
        success = True
    finally:
        return {'success':success,
                'tb':tb,
                'msg':msg} if not success else {'success':success}

替代方案：

def foo():
    result = {"success": False}
    try:
        pass
    except FirstException:
        result['tb'] = traceback.format_exc()
        result['msg'] = 'There was FirstExc'
    except SecondException:
        result['tb'] = traceback.format_exc()
        result['msg'] = 'There was SecondExc'
    else:
        result['success'] = True
    finally:
        return result

上述略有不同：

def foo():
    result = {"success": False}
    try:
        pass
    except FirstException:
        result.update({'tb': traceback.format_exc(), 'msg': 'There was FirstExc'})
    except SecondException:
        result.update({'tb': traceback.format_exc(), 'msg': 'There was SecondExc'})
    else:
        result['success'] = True
    finally:
        return result