---
id: python-operators-membership
title: "Python Operators Membership"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["in operator", "not in operator", "파이썬 멤버십 연산자"]
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", "operators", "membership"]
raw_sources: ["https://www.w3schools.com/python/python_operators_membership.asp"]
applied_in: []
github_commit: ""
---

# [[Python Operators Membership]]

## 🎯 한 줄 통찰 (One-line insight)
`in`/`not in` test whether a value exists within any sequence — lists and strings alike — using identical syntax. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`in`** — True if a specified value is present in the sequence. [S1]
- **`not in`** — True if a specified value is NOT present in the sequence. [S1]
- **Works across sequence types** — lists and strings both support membership testing. [S1]

## 📖 세부 내용 (Details)
- List membership: `fruits = ["apple", "banana", "cherry"]; print("banana" in fruits)`. [S1]
- List non-membership: `print("pineapple" not in fruits)`. [S1]
- String membership: `text = "Hello World"; print("H" in text); print("hello" in text)  # False, case-sensitive; print("z" not in text)`. [S1]

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

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 이미 Python Strings 챕터에서 문자열 대상 `in`이 선행 소개되었고, 여기서 리스트로 확장된다. [S1]

## 💻 코드 패턴 (Code patterns)
Membership test on a list (Python):
```python
fruits = ["apple", "banana", "cherry"]
print("banana" in fruits)
print("pineapple" not in fruits)
```

## ✅ 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 Strings]], [[Python Lists]], [[Python If Else]]
- **참조 맥락:** 시퀀스(리스트/문자열)에 값이 존재하는지 확인할 때 사용.

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

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