try -> except -> else -> except?

[Bruno Desthuilliers]

David House a écrit :
> Hi all,
> 
> I'm looking for some structure advice. I'm writing something that
> currently looks like the following:
> 
> try:
>     <short amount of code that may raise a KeyError>
> except KeyError:
>     <error handler>
> else:
>     <nontrivial amount of code>
> 
> This is working fine. However, I now want to add a call to a function
> in the `else' part that may raise an exception, say a ValueError.

If your error handler terminates the function (which is usually the case 
when using the else clause), you can just skip the else statement, ie:

try:
     <short amount of code that may raise a KeyError>
except KeyError:
     <error handler with early exit>
<nontrivial amount of code>

Then adding one or more try/except is just trivial.


> So I
> was hoping to do something like the following:
> 
> try:
>     <short amount of code that may raise a KeyError>
> except KeyError:
>     <error handler>
> else:
>     <nontrivial amount of code>
> except ValueError:
>     <error handler>
> 
> However, this isn't allowed in Python.

Nope. But this is legal:


try:
     <short amount of code that may raise a KeyError>
except KeyError:
     <error handler>
else:
     try:
         <nontrivial amount of code>
     except ValueError:
         <error handler>



> An obvious way round this is to move the `else' clause into the `try'

"obvious" but not necessarily the best thing to do.

(snip - cf above for simple answers)