[Baypiggies] len(iterable)

[Shannon -jj Behrens]

On Wed, Aug 6, 2008 at 1:34 PM, Shannon -jj Behrens <jjinux at gmail.com> wrote:
> On Wed, Aug 6, 2008 at 1:11 PM, Tung Wai Yip <tungwaiyip at yahoo.com> wrote:
>> I can think of 2 ways,
>>
>>>>> it = xrange(10)
>>>>> len(list(it))
>> 10
>>
>>>>> it = xrange(10)
>>>>> sum(1 for i in it)
>> 10
>>
>> Wai Yip
>>
>>
>>> I have an iterable, and I want to find out how long it is.  I don't
>>> care if it consumes the iterable.  Furthermore, I know the iterable is
>>> not infinite.  Consider:
>>>
>>>>>> len((i for i in xrange(10)))
>>> Traceback (most recent call last):
>>>   File "<stdin>", line 1, in <module>
>>> TypeError: object of type 'generator' has no len()
>>>
>>> It makes sense that len() not be defined, but I can't seem to find a
>>> simple count function.  Of course, I can write one, but it seems like
>>> it should exist in itertools or something.  (By the way, the count
>>> function in itertools is something completely different.)
>>>
>>> Thanks,
>>> -jj
>
> I can't do len(list(iter)) because I don't have enough RAM ;)  Guido
> and Wai Yip's idea was the most elegant.  It seems strange that this
> isn't in the standard library.

By the way, my rather boring solution was:

def iter_len(iter):
    """Return the length of the given iterator.

    len(iter) doesn't work in cases such as::

        len((i for i in xrange(10)))

    I can't find anything for this in the standard library.

    """
    count = 0
    for i in iter:
        count += 1
    return count


def test_iter_len():
    assert_equal(iter_len(xrange(5)), 5)


Gees, I'm so boring sometimes!

-jj

-- 
Lisp programmers know the value of everything, but the cost of nothing...
On my Lisp, '() costs 4 bytes.
http://jjinux.blogspot.com/