---
id: python-class-properties
title: "Python Class Properties"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["instance properties", "class properties", "파이썬 클래스 속성"]
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", "class-properties"]
raw_sources: ["https://www.w3schools.com/python/python_class_properties.asp"]
applied_in: []
github_commit: ""
---

# [[Python Class Properties]]

## 🎯 한 줄 통찰 (One-line insight)
A property defined inside `__init__()` belongs to each individual object, but one defined directly in the class body is shared across ALL instances — changing it via `ClassName.prop = value` updates what every object sees, even ones created before the change. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Instance property** — defined via `self.x = ...` inside `__init__()`; unique per object. [S1]
- **Class property** — defined directly in the class body (not inside a method); shared by ALL instances. [S1]
- **Dot notation access** — `obj.property`. [S1]
- **Modifying properties** — `p1.age = 26` changes just that instance. [S1]
- **`del obj.property`** — deletes a property from a specific object. [S1]
- **Modifying a CLASS property** — `Person.lastname = "Refsnes"` affects every instance, including ones already created. [S1]
- **Adding properties dynamically** — `p1.age = 25` adds a property to just that one object, not to the class. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Class-level mutation is retroactive** — because a class property is shared storage, not copied per instance, changing it via the class name propagates to every existing object immediately — a common source of surprise bugs if mistaken for an instance property. [S1]

## 📖 세부 내용 (Details)
- Instance property: `class Person: def __init__(self, name, age): self.name = name; self.age = age`. [S1]
- Delete a property: `del p1.age` — `p1.name` still works, but `p1.age` now errors. [S1]
- Class vs. instance property: `class Person: species = "Human"; def __init__(self, name): self.name = name` — `species` shared, `name` per-instance. [S1]
- Modifying a class property: `Person.lastname = "Refsnes"` — affects `p1.lastname` and `p2.lastname` both. [S1]
- Dynamic per-object addition: `p1.age = 25; p1.city = "Oslo"` — only affects `p1`. [S1]

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

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 클래스 속성은 모든 인스턴스가 공유해야 하는 설정값(예: 종(species))에 쓰이고, 인스턴스 속성은 객체별 고유 데이터에 쓰인다. [S1]

## 💻 코드 패턴 (Code patterns)
Class property shared across all instances (Python):
```python
class Person:
    lastname = ""  # class property
    def __init__(self, name):
        self.name = name  # instance property

p1 = Person("Linus")
p2 = Person("Emil")
Person.lastname = "Refsnes"
print(p1.lastname)  # Refsnes
print(p2.lastname)  # Refsnes
```

## ✅ 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 Class Init Method]], [[Python Class Methods]], [[Python Encapsulation]]
- **참조 맥락:** 인스턴스 속성 vs 클래스 속성의 차이 — 공유 상태와 개별 상태를 구분해야 한다.

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

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