Apa perbedaan antara iterable lan iterator?

Question

Accepted Answer

An **iterable** adalah apa wae sing bisa dipulungi (list, string, dict); an **iterator** adalah obyek sing nindakake iterasi sejati, nggawe nilai siji-siji lan nyacat posisine. Bedanya iki nedhi cara `for` loop bisa ngomong ing Python.

## Rong protokol

```text
Iterable → has __iter__()  → returns an iterator
Iterator → has __next__()  → returns the next value (and __iter__ returning itself)
```

## Carane for loop sejati

```python
# this for loop...
for x in [1, 2, 3]:
    print(x)

# ...is roughly equivalent to:
it = iter([1, 2, 3])    # __iter__ → get an iterator from the iterable
while True:
    try:
        x = next(it)     # __next__ → get the next value
        print(x)
    except StopIteration: # raised when exhausted → loop ends
        break
```

A `for` loop nyamet `iter()` kanggo entuk iterator, banjur ketok-ketok nyamet `next()` nganti `StopIteration` tandha pungkasane. Protokol iki sing ndadekake apa wae iterable bisa dipulungi.

## Iterable vs iterator ing praktik

```python
nums = [1, 2, 3]        # an ITERABLE (a list)
it = iter(nums)         # an ITERATOR over it

next(it)   # 1
next(it)   # 2
next(it)   # 3
next(it)   # StopIteration

# the list is REUSABLE (get a fresh iterator each loop);
# an iterator is CONSUMED ONCE — exhausted after one pass
list(it)   # [] — already used up
```

Beda kunci: iterable (list) bisa dipulungi akeh kali (saben `for` entuk iterator anyar); iterator **sekali-pakai** — sawise habis, kosong.

## Bangun iterator khusus

```python
class Countdown:
    def __init__(self, start): self.n = start
    def __iter__(self): return self          # the iterable returns itself as iterator
    def __next__(self):
        if self.n <= 0:
            raise StopIteration               # signal the end
        self.n -= 1
        return self.n + 1

for x in Countdown(3):   # 3, 2, 1
    print(x)
```

## Generator yaiku iterator

```python
def gen(): yield 1; yield 2     # a generator function returns an iterator automatically
```

Generator yaiku cara gampang nggawe iterator — `yield` ngomong mesin `__next__`/`StopIteration` kanggo sampeyan.

## Kenapa penting

Bedane iterable/iterator njlentrehake **carane `for` loop bisa omong** ing Python lan carane iterasi dipersatua ing kabeh koleksyon (list, dict, file, generator) liwat protokol iterator.

Pamahaman iki njlentrehake prilaku sejati — kenapa iterator mung bisa dikonsumsi sekali (bug umum: pulungi generator/zip rong kali entuk ora apa apa kekarangan), kenapa generator yaiku iterator, lan carane nggawe obyek sarili iterable.

Protokoliki fondasi model iterasi Python sing elegan, konsisten lan penting kanggo makarya karo generator, evaluasi langsun, lan klas iterable khusus.