[Python-3000] try ... then ... then ... except / finally

[Antoine]

> Can you explain the difference to:
>
> try:
>      self.db_transaction.commit()
>      self.tmpoutfile.close()
>      self.destroy_shared_memory_handle()
> except Exception, e:
>      logging.error("an exception occurred in cleanup: %s", e)

In your construct, if self.db_transaction.commit() raises an exception,
self.tmpoutfile won't get closed and self.destroy_shared_memory_handle()
won't be called.

In my proposal, if an exception is raised in a "try" block, the execution
skips to the next "then" block, and so on.
At the end it executes the "except" block if at least one "try" or "then"
block raised an exception.