[Zope3-dev] Please, no bare 'except:' clauses!

[Jim Fulton]

Guido van Rossum wrote:
>>Maybe we should start documenting places where bare except is
>>acceptable and where it isn't.  Not as an exclusive list, but as a
>>helpful guide for programmers to decide when to use it and when not
>>to use it.  Here's a start of some places where I think bare except
>>is okay:
>>
>>- To do additional processing whenever an exception in a sub-call
>>  occurs.  In this case you always re-raise the original exception
>>  after doing the processing.  E.g.
>>
>>  txn = a_bdb_transaction()
>>  try:
>>      val = do_some_work()
>>  except:
>>      txn.abort()
>>      raise
>>  else:
>>      txn.commit()
>>      return val
>>
> 
> I would prefer to write that as follows:
> 
>   txn = a_bdb_transaction()
>   ok = 0
>   try:
>     val = do_some_work()
>     ok = 1
>   finally:
>     if ok:
>       txn.commit()
>     else:
>       txn.abort()
>   return val

Why is that? The former looks cleaner to me.

At first glance, the logic looked wrong to me.  I had
to think a bit to realize that it propigates the exception that
is raised and that it only returns a value if there is no exception.

Jim

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