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clever exit of nested loops


Christian Gollwitzer wrote:

> Am 26.09.18 um 12:28 schrieb Bart:
>> On 26/09/2018 10:10, Peter Otten wrote:
>>> class Break(Exception):
>>> pass
>>>
>>> try:
>>> for i in range(10):
>>> print(f'i: {i}')
>>> for j in range(10):
>>> print(f'\tj: {j}')
>>> for k in range(10):
>>> print(f'\t\tk: {k}')
>>>
>>> if condition(i, j, k):
>>> raise Break
>>> except Break:
>>> pass
>>>
>> 
>> For all such 'solutions', the words 'sledgehammer' and 'nut' spring to
>> mind.
>> 
>> Remember the requirement is very simple, to 'break out of a nested loop'
>> (and usually this will be to break out of the outermost loop). What
>> you're looking is a statement which is a minor variation on 'break'.
> 
> Which is exactly what it does. "raise Break" is a minor variation on
> "break".
> 
>> Not
>> to have to exercise your imagination in devising the most convoluted
>> code possible.
> 
> To the contrary, I do think this solution looks not "convoluted" but
> rather clear. Also, in Python some other "exceptions" are used for a
> similar purpose - for example "StopIteration" to signal that an iterator
> is exhausted. One might consider to call these "signals" instead of
> "exceptions", because there is nothing exceptional, apart from the
> control flow.
> 
> Christian
> 
> 

I've done the same before myself (exit from nested blocks to a containing 
block using exception), but it does violate the principle "Exceptions should 
be used for exceptional conditions).