How to count the items in a generator consumed by other code

If you don't care that you are consuming the generator, you can just do:

sum(1 for x in gen)

Usually, I'd just turn the generator into a list and take its length. If you have reasons to assume that this will consume too much memory, your best bet indeed seems to be the wrapper class you suggested yourself. It's not too bad, though:

class CountingIterator(object):
    def __init__(self, it):
        self.it = it
        self.count = 0
    def __iter__(self):
        return self
    def next(self):
        nxt = next(self.it)
        self.count += 1
        return nxt
    __next__ = next

(The last line is for forward compatibility to Python 3.x.)

Here is another way using itertools.count() example:

import itertools

def generator():
    for i in range(10):
       yield i

def process(l):
    for i in l:
        if i == 5:
            break

def counter_value(counter):
    import re
    return int(re.search('\d+', repr(counter)).group(0))

counter = itertools.count()
process(i for i, v in itertools.izip(generator(), counter))

print "Element consumed by process is : %d " % counter_value(counter)
# output: Element consumed by process is : 6

Hope this was helpful.