Does python iterable imply countable?

Question

I've stumbled upon an interesting case - only thing I am sure about is that I will get an iterable object.

What I really, and only, want to do is to count it.

I've searched if iterable in python implies countable and I found various places claiming so, except the official docs.

So 2 questions arise:

In Python, does iterable => countable (number of items)? Or is it just very common to be so?
Is there a generic pythonic way to get count from an iterable? Which seems to be answered here https://stackoverflow.com/a/3345807/1835470 i.e. not without counting, but author provided a pythonic one-liner:
```
sum(1 for _ in iterableObject)
```

An iterable might be infinitely long, for example `itertools.count()`. — Veedrac, Apr 16 '20 at 07:05
Well, it could be countably infinite, sure. But that's probably not what you mean. Btw, what do you mean "not with counting"? What exactly do you mean by counting? — juanpa.arrivillaga, Apr 16 '20 at 07:07
@juanpa.arrivillaga I guess bad choice of words - I meant looping/iterating over and counting the iterations — jave.web, Apr 16 '20 at 07:12
@juanpa.arrivillaga yes I know, and I was asking if there's a way without doing it yourself with the oneliner :) — jave.web, Apr 20 '20 at 11:27

score 0 · Answer 1 · answered Apr 16 '20 at 07:07

0

iterables do not support the len method. To get their length you have to cast them into something that does support it or manually loop through them (and exhaust them in the process) while counting such as in this code snippet you posted.

As a result, the requirement of using an iterable and needing to know its length is somewhat conflicting. Plus as @Veedrac says in the comments, iterables can have infinite length.

To sum up, if you need to know how many items are contained, you need a different data structure.

answered Apr 16 '20 at 07:07

Ma0

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you mean don't support len() call on them by default right? The structure is however just fine - sometimes there is no need to know the length and sometimes it is (which can happen in regular cases of list - that said, list in particular supports both) – jave.web Apr 16 '20 at 07:18

Does python iterable imply countable?

1 Answers1