[Tutor] I don't understand example 12.10.2

[Jeff Shannon]

Daniel Nash wrote:

> and what is going on here?
>
>            try:
>                data = StringIO.StringIO()
>                mimetools.decode(file, data, submsg.getencoding())
>            except ValueError:
>                continue 


Magnus already told you about StringIO, so I won't repeat that.  For the 
rest of it, this fragment is hard to analyze out of context.  It looks 
like this must be a segment of a loop, because 'continue' is only valid 
within a loop.  What you have here is an exception block.  Python tries 
to run the code within the 'try:' segment of the block, and that's all 
that runs if there's no errors detected.  However, if something in that 
segment has a problem, it can throw an exception.  Exceptions will 
normally stop your program, unless you catch them, which is what the 
'except' segment is supposed to do.  In this case, if there is an 
exception that is of type 'ValueError', then Python will run the 
specified bit of code in an attempt to let you recover from the error. 
 The recovery, in this case, consists only of 'continue',  which 
immediately returns to the top of your loop and begins the next 
iteration of the loop, essentially throwing away whatever has been done 
so far (since it's somehow invalid, presumably because of a bad submsg).

In other words, paraphrasing this fragment in English, it would be 
something like:  "Try to decode the submessage into a new StringIO 
file-like object.  If you run into any invalid values, then skip it and 
start over again with the next submessage."  (I am, of course, only 
guessing that the loop iterates over submessages, since you didn't show 
the beginning of the loop...)

Jeff Shannon
Technician/Programmer
Credit International