---
id: python-inner-classes
title: "Python Inner Classes"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["nested class", "파이썬 내부 클래스"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.88
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["python", "programming", "w3schools", "inner-class", "nested-class"]
raw_sources: ["https://www.w3schools.com/python/python_class_inner.asp"]
applied_in: []
github_commit: ""
---

# [[Python Inner Classes]]

## 🎯 한 줄 통찰 (One-line insight)
An inner class defined inside another does NOT automatically get access to the outer instance — the outer object must explicitly pass itself as an argument to the inner class for the inner class to reach the outer's data. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Inner class** — a class defined inside another class. [S1]
- **Purpose** — grouping helper classes that are only used within the outer class's context, improving organization. [S1]
- **Accessing from outside** — `outer = Outer(); inner = outer.Inner(); inner.display()`. [S1]
- **No automatic outer access** — inner classes do NOT automatically see the outer instance; the outer instance must be passed explicitly as a parameter. [S1]
- **Multiple inner classes** — a class can contain several inner classes (e.g. `Computer` containing `CPU` and `RAM`). [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Self-referential composition** — `self.engine = self.Engine()` inside `Car.__init__` is the idiomatic way to instantiate an inner class as a property of the outer instance, giving each `Car` object its own `Engine` sub-object. [S1]

## 📖 세부 내용 (Details)
- Basic inner class access: `outer = Outer(); inner = outer.Inner(); inner.display()`. [S1]
- Passing outer instance for access: `class Inner: def __init__(self, outer): self.outer = outer; def display(self): print(f"Outer class name: {self.outer.name}")`; created via `inner = outer.Inner(outer)`. [S1]
- Practical composition example: `Car` class instantiates its own `Engine` inner class as `self.engine = self.Engine()`, then `car.engine.start()` controls the sub-object. [S1]
- Multiple inner classes: `Computer` class with `self.cpu = self.CPU()` and `self.ram = self.RAM()`. [S1]

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

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — Car의 Engine, Computer의 CPU/RAM처럼 "부품" 관계를 표현하는 컴포지션 패턴에 표준적으로 쓰인다. [S1]

## 💻 코드 패턴 (Code patterns)
Self-referential inner class composition (Python):
```python
class Car:
    def __init__(self, brand, model):
        self.brand = brand
        self.model = model
        self.engine = self.Engine()
    class Engine:
        def __init__(self):
            self.status = "Off"
        def start(self):
            self.status = "Running"

car = Car("Toyota", "Corolla")
car.engine.start()
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.88
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[Python Tutorial]]
- **관련 개념:** [[Python Classes]], [[Python Class Init Method]]
- **참조 맥락:** 부품(has-a) 관계를 표현하는 클래스 구성 패턴 — OOP 챕터의 마지막 개념.

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

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