[python] Getting number of elements in an iterator in Python

Although it's not possible in general to do what's been asked, it's still often useful to have a count of how many items were iterated over after having iterated over them. For that, you can use jaraco.itertools.Counter or similar. Here's an example using Python 3 and rwt to load the package.

$ rwt -q jaraco.itertools -- -q
>>> import jaraco.itertools
>>> items = jaraco.itertools.Counter(range(100))
>>> _ = list(counted)
>>> items.count
100
>>> import random
>>> def gen(n):
...     for i in range(n):
...         if random.randint(0, 1) == 0:
...             yield i
... 
>>> items = jaraco.itertools.Counter(gen(100))
>>> _ = list(counted)
>>> items.count
48