Raise X or Raise X()?

[James Elford]

On 11/03/12 19:04, bvdp wrote:
> Which is preferred in a raise: X or X()? I've seen both. In my specific case I'm dumping out of a deep loop:
> 
> try:
>   for ...
>     for ...
>       for ...
>         if match:
>            raise StopInteration()
>          else ...
> 
> except StopInteration:
>    print "found it"

I wonder whether you need to use an exception here rather than a yield
statement? Exceptions should reflect Exceptional circumstances (and come
with associated stack trace, and so on...). The following should do
something like what you want, without raising exceptions.

>>> # Deeply loop into a collection of collections
>>> def find(collection):
...    for sub_col in collection:
...        for item in sub_col:
...            for foo in item.list_field:
...                if foo.is_match:
...                    yield foo

>>> # Some junk classes to iterate over
>>> class Item(object):
...    def __init__(self, some_range):
...        self.list_field = [ListedItem(i) for i in some_range]

>>> class ListedItem(object):
...    def __init__(self, number):
...        self.tag = number
...        self.is_match = False

>>>    def __str__(self):
...        return str(self.tag)

>>> # Construct a list of items
>>> l = [[Item(range(i)) for i in range(10)],
...	[Item(range(i, 2*i)) for i in range(10,20)]]

>>> l[0][9].list_field[3].is_match = True

>>> for i in find(l):
...     print(i)
3

James