---
id: python-functions
title: "Python Functions"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["def keyword", "파이썬 함수"]
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", "functions"]
raw_sources: ["https://www.w3schools.com/python/python_functions.asp"]
applied_in: []
github_commit: ""
---

# [[Python Functions]]

## 🎯 한 줄 통찰 (One-line insight)
A function reaching `return` stops executing immediately and sends the value back; a function with no `return` statement at all simply returns `None`. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Function** — a reusable block of code that only runs when called; helps avoid repetition. [S1]
- **`def` keyword** — defines a function: `def my_function(): ...`. [S1]
- **Function naming** — same rules as variables (start with letter/underscore, alphanumeric+underscore only, case-sensitive). [S1]
- **`return`** — sends a value back and immediately stops execution. [S1]
- **No return → `None`** — a function without a return statement returns `None` by default. [S1]
- **`pass`** — required for a syntactically empty function body. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **DRY via functions** — the canonical motivating example is replacing repeated Fahrenheit→Celsius conversion code with one `fahrenheit_to_celsius()` function called multiple times. [S1]

## 📖 세부 내용 (Details)
- Basic definition and call: `def my_function(): print("Hello from a function"); my_function()`. [S1]
- Reusable calculation: `def fahrenheit_to_celsius(fahrenheit): return (fahrenheit - 32) * 5 / 9`. [S1]
- Using the return value directly: `print(get_greeting())`. [S1]
- Empty placeholder: `def my_function(): pass`. [S1]

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

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 이후 Arguments/Scope/Lambda/Recursion/Generators 챕터 전체의 기초가 되는 개론이다. [S1]

## 💻 코드 패턴 (Code patterns)
Reusable function replacing repeated code (Python):
```python
def fahrenheit_to_celsius(fahrenheit):
    return (fahrenheit - 32) * 5 / 9

print(fahrenheit_to_celsius(77))
print(fahrenheit_to_celsius(95))
```

## ✅ 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 Arguments]], [[Python Scope]], [[Python Lambda]]
- **참조 맥락:** 함수 챕터군 전체의 진입점.

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

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