On 2009-02-10, Albert Hopkins <mar...@letterboxes.org> wrote:
> On Tue, 2009-02-10 at 12:50 -0800, Josh Dukes wrote:
>
> I don't understand what you mean by this. But if you really want to
> know if a generator is "non-empty":
>
> def non_empty(virgin_generator):
> try:
> virgin_generator.next() # note you just lost the first value
> return True
> except StopIteration:
> return False
>
> The only way to get around this is to put all the values of a generator
> inside a container (e.g. a list):
>
> l = list(generator_object)
>
> but in doing so you've (obviously) lost the advantages of the generator.
Well he could always use a wrapper like the following:
nothing = object()
class BoolIterator (object):
def __init__(self, iter):
self.iter = iter
self.value = nothing
self.item = nothing
def __iter__(self):
return (self)
def __nonzero__(self):
if self.value is nothing:
try:
self.item = self.iter.next()
self.value = True
return True
except StopIteration:
self.value = False
return False
else:
return self.value
def next(self):
if self.item is not nothing:
result = self.item
self.item = nothing
return result
if self.value is not nothing:
return self.iter.next()
else:
try:
result = self.iter.next()
self.value = True
return result
except StopIteration:
self.value = False
raise
it1 = BoolIterator(i for i in xrange(10))
for i in it1:
print i
it2 = BoolIterator(i for i in xrange(10))
if it2:
print "item found"
for i in it2:
print i
else:
print "problem"
it3 = BoolIterator(i for i in xrange(0))
if it3:
print "problem"
else:
print "it3 is empty"
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