Re-raise confusion

Question

What is the best approach if I call a function (e.g. foo()) that may raise ValueError or AttributeError, and in case of ValueError I want to provide another way (e.g. call bar()), but in case of AttributeError I want to re-raise the exception?

1. Re-raise a specific (here AttributeError) exception explicitly?

    try:
        foo() # may raise ValueError or AttributeError
    except ValueError:
        bar()
    except AttributeError:
        raise
   

2. or just do nothing (re-reises implicitly)?

    try:
        foo() # may raise ValueError or AttributeError
    except ValueError:
        bar()
   

Update 1:

What is the better approach in case of writing a library (at least a module I know it'll be used by different users)? Explicitly re-raise and document the function that re-raises or just document the function (writing that it may implicitly raise a specific exception)?

Answer 1

You can just except the exception without re-raising. In your case, this is not necessary:

 try:
     foo() # may raise ValueError or AttributeError
 except ValueError:
     bar()

Raising again would be useful in a case where you would have to do some cleanup or need to call a function before raising like:

 try:
     foo() # may raise ValueError or AttributeError
 except ValueError:
     bar()

     raise