处理python中的递归错误回溯

Question

I'm working on implementing a small programming languge in Python for the hell of it, and the language's execution basically consists of recursive calls to a function called execute . I've implemented my own error handling, but in order to have that error handling work I need to catch some exceptions and throw them as my own types, resulting in code that looks something like this:

def execute(...):
    try:
        try:
            # do stuff
        except IndexError:
            raise MyIndexError()
    except MyErrorBase as e:
        raise MyErrorBase(e, newTracebackLevel) # add traceback level for this depth

I really hate the nested try blocks... is there any way to fix this?

Answer 1

You need to set try statements when ever needed.

Put it only on start of execution.

try statement is basically is a longjump. You want to do some long tasks which may fail at any place in the code it can be in inner calls. longjump helps you to catch fails.

In lua language there's method called pcall. (protected call) Whenever it invokes at error the call returns error status and error message is taken as the second return value.

Answer 2

If you really want to do this, try creating a mapping between base exception types and your new exception types:

exceptionMap = {
   IndexError: MyIndexError,
   # ...
}

def execute(...):
    try:
        # do stuff
    except tuple(exceptionMap) as e:
        raise exceptionMap[type(e)](e, newTracebackLevel)

Example:

In [33]: exceptionMap = {IndexError: RuntimeError}

In [34]: a = []

In [35]: try:
    ...:     a[1]
    ...: except tuple(exceptionMap) as e:
    ...:     raise exceptionMap[type(e)](str(e))

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-35-bc6fdfc44fbe> in <module>()
      2     a[1]
      3 except tuple(exceptionMap) as e:
----> 4     raise exceptionMap[type(e)](str(e))
      5
      6

RuntimeError: list index out of range