bokr at oz.net
Tue Jan 10 21:54:44 CET 2006
On Tue, 10 Jan 2006 18:37:13 GMT, "Andrew Koenig" <ark at acm.org> wrote:
>Can anyone think of an easy technique for creating an object that acts like
>a generator but has additional methods?
>For example, it might be nice to be able to iterate through an associative
>container without having to index it for each element. Right now, I can say
> i = iter(d)
>and then repeatedly calling i.next() gives us the keys for the elements.
>But to get the corresponding value requires us to look up the key.
>Of course one could define a generator that yields key-value pairs, along
>the following lines:
> def kviter(d):
> for i in d:
> yield i, d[i]
>to hide the lookup. But this yields a tuple even when you don't want it.
>In other words, I must now write
> for k, v in kviter(d):
> # whatever
>and I can think of situations in which I don't really want both the key and
>the value all the time.
>So what I really want is something like this:
> it = augiter(d)
> for i in it:
> if <some condition on i>:
>In other words, I want "it" to support both the next and value methods (or
>next and something else)
>Of course I can write such a beast as a class, but that prevents me from
>taking advantage of the yield statement in its implementation.
It does? (this just occurred to me, so there may be some gotcha ;-)
>>> class augiter(object):
... def __init__(self, d): self.d = d
... def __iter__(self):
... for k in self.d: self.value = self.d[k]; yield k
>>> it = augiter(dict(enumerate('abcd')))
>>> for i in it:
... if i%2: print i, it.value
You could of course store self._value and def value(self):return self._value to be closer to your syntax)
>So my question is: Can you think of an easy way to write something that
>looks like a generator (using yield), but can also incorporate methods other
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