---
id: python-iterators
title: "Python Iterators"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["iterator protocol", "__iter__", "__next__", "파이썬 이터레이터"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["python", "programming", "w3schools", "iterators", "iterable"]
raw_sources: ["https://www.w3schools.com/python/python_iterators.asp"]
applied_in: []
github_commit: ""
---

# [[Python Iterators]]

## 🎯 한 줄 통찰 (One-line insight)
An iterable (list, tuple, string, etc.) is a container you can get an iterator FROM via `iter()`; a custom class becomes its own iterator by implementing `__iter__()` (return self) and `__next__()` (return the next value, raising StopIteration to terminate). [S1]

## 🧠 핵심 개념 (Core concepts)
- **Iterator** — an object implementing the iterator protocol (`__iter__()` and `__next__()`); contains a countable number of values. [S1]
- **Iterable vs. iterator** — lists/tuples/dicts/sets are iterable (have an `iter()` method to GET an iterator); the iterator itself is what `next()` advances. [S1]
- **`iter()`** — returns an iterator from an iterable object. [S1]
- **`next()`** — advances the iterator one step, returning the next value. [S1]
- **for loop internals** — a for loop actually creates an iterator object internally and calls `next()` on each pass. [S1]
- **Custom iterator class** — implement `__iter__()` (must return the iterator object itself) and `__next__()` (must return the next value in sequence). [S1]
- **`StopIteration`** — raised inside `__next__()` to signal the end, preventing infinite iteration in a for loop. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Without StopIteration, custom iterators run forever in a for loop** — the example shows that a `__next__()` with no terminating condition would loop forever if placed in a `for` loop (unlike manual `next()` calls, which just stop when you stop calling them). [S1]

## 📖 세부 내용 (Details)
- Get iterator from a tuple: `mytuple = ("apple","banana","cherry"); myit = iter(mytuple); print(next(myit))`. [S1]
- Custom iterator class: [S1]
```python
class MyNumbers:
    def __iter__(self):
        self.a = 1
        return self
    def __next__(self):
        x = self.a
        self.a += 1
        return x
```
- With StopIteration to prevent infinite loop: `if self.a <= 20: ... else: raise StopIteration`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
소스에서 모순되는 정보는 발견되지 않음.

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — Python Generators 챕터의 `yield`가 이 이터레이터 프로토콜을 훨씬 간결하게 구현하는 대안이다. [S1]

## 💻 코드 패턴 (Code patterns)
Custom iterator with a StopIteration terminating condition (Python):
```python
class MyNumbers:
    def __iter__(self):
        self.a = 1
        return self
    def __next__(self):
        if self.a <= 20:
            x = self.a
            self.a += 1
            return x
        else:
            raise StopIteration

myclass = MyNumbers()
myiter = iter(myclass)
for x in myiter:
    print(x)
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[Python Tutorial]]
- **관련 개념:** [[Python Generators]], [[Python For Loops]], [[Python Classes]]
- **참조 맥락:** for 루프가 내부적으로 사용하는 프로토콜 — Generators가 이를 간결화한 대안이다.

## 📚 출처 (Sources)
- [S1] W3Schools — Python Iterators — https://www.w3schools.com/python/python_iterators.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "Python Iterators" page (Astra wiki-curation, P-Reinforce v3.1 format).