[Tutor] Skipping elements from inside generator loops

[Gregor Lingl]

>
>
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>cat_list = [ cat for cat in procession if cat != 'ALARM!' and cat !=
>>'the evil dog' ] for cat in cat_list:
>>	print cat
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>    
>>
>
>Ah, but this is cheating - you are looking for 'the evil dog' directly.
>You 
>are only allowed to check for the alarm, not for the dog itself!
>
>Y, Scot
>  
>
What about this:

 >>> p = ['black cat',
             'white cat',
             'grey cat',
             'ALARM!',
             'the evil dog',
             'fat cat',
             'slow cat']

Now one observes, that in

 >>> zip([None]+p,p)
[(None, 'black cat'), ('black cat', 'white cat'), ('white cat', 'grey 
cat'),
('grey cat', 'ALARM!'), ('ALARM!', 'the evil dog'), ('the evil dog', 
'fat cat'),
 ('fat cat', 'slow cat')]

the second Element of each pair is good if only 'ALARM!' does not occur 
in the pair:

 >>> [pair[1] for pair in zip([None]+p,p) if 'ALARM!' not in pair]
['black cat', 'white cat', 'grey cat', 'fat cat', 'slow cat']

Not very elegant! Amendments?

Gregor