If/then style question

[Ethan Furman]

Rob Richardson wrote:
> My thanks for pointing out the existence of the else: suite in the for
> statement.  However, I remain confused.  For reference, here's the
> original code:
> 
>> def myMethod():
>>     for condition, exitCode in [
>>             (cond1, 'error1'),
>>             (cond2, 'very bad error'),
>>     ]:
>>         if not condition:
>>             break
>>     else:
>>        do_some_usefull_stuff() # executed only if the we never hit the
> 
>> break statement.
>>        exitCode = good1
>>
>>     return exitCode
> 
> What do we know about cond1 and cond2?  Do they have to be assigned
> before this for statement is executed?  The sample code doesn't show it.

cond1 and cond2 should be expressions of some sort, e.g.  check_files() 
or feedback (feedback being a variable of some sort).


> The loop is going to to execute once for condition = cond1 and exitCode
> = 'error1'.  The only thing it's going to do is check to see what
> condition is.  Since we can assume (I hope) that cond1 is not false,
> then the for loop continues.  Now condition = cond2 and exitCode = 'very
> bad error'.  The if condition is still false, so the loop continues.
> We've come to the end now, and the else: suite is executed.  We finally
> do some useful stuff and exitCode = good1.  (Should that have been in
> quotes, or doesn't it matter?)  But now the for loop's job is done and
> we return the exitCode, which at this point is good1.  
> 
> But I still don't understand what happens if we can't do useful stuff.
> Where does an error code get set, and where is that error code checked?
> We don't have a chance to check it in the for loop, because once we're
> in the else: suite the loop condition is never rechecked.  Or is it?

You have outlined what happens when cond1 and cond2 both evaluate to 
True -- what happens if, say, cond2 evaluates to False?

.

.

.

.

.

if not cond2 becomes True, we hit the break, do not do 
do_some_usefull_stuff(), but proceed to return exitCode -- and exitCode 
was set in the for loop to 'very bad error' when condition was set to cond2.

The exitCode no longer needs to be checked inside the function, because 
there is no chance of do_some_useful_stuff running if any of the 
conditions are False.

Hope this helps.

~Ethan~