---
id: python-regex
title: "Python RegEx"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["re module", "regular expressions", "파이썬 정규식"]
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", "regex", "re"]
raw_sources: ["https://www.w3schools.com/python/python_regex.asp"]
applied_in: []
github_commit: ""
---

# [[Python RegEx]]

## 🎯 한 줄 통찰 (One-line insight)
The `re` module's four core functions each answer a different question — findall() (all matches as a list), search() (first Match object or None), split() (list split at matches), sub() (replace matches) — and a Match object itself carries `.span()`, `.string`, `.group()` for inspecting what actually matched. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`re` module** — Python's built-in package for regular expressions. [S1]
- **`re.findall(pattern, txt)`** — returns a list of ALL matches (empty list if none). [S1]
- **`re.search(pattern, txt)`** — returns a Match object for the FIRST match, or `None` if no match. [S1]
- **`re.split(pattern, txt, maxsplit)`** — splits the string at each match; `maxsplit` limits the split count. [S1]
- **`re.sub(pattern, repl, txt, count)`** — replaces matches; `count` limits replacements. [S1]
- **Metacharacters** — `[]` set, `\` special sequence/escape, `.` any char, `^` starts-with, `$` ends-with, `*`/`+`/`?` occurrence counts, `{}` exact count, `|` or, `()` group. [S1]
- **Special sequences** — `\d` digit, `\D` non-digit, `\s` whitespace, `\S` non-whitespace, `\w` word char, `\W` non-word char, `\b`/`\B` word boundary, `\A`/`\Z` string start/end. [S1]
- **Flags** — `re.IGNORECASE`, `re.MULTILINE`, `re.DOTALL`, etc. [S1]
- **Match object properties** — `.span()` (start/end tuple), `.string` (original input string), `.group()` (the matched substring). [S1]

## 📖 세부 내용 (Details)
- Basic search: `x = re.search("^The.*Spain$", txt)`. [S1]
- All matches: `x = re.findall("ai", txt)`. [S1]
- First match only: `x = re.search("\s", txt); x.start()`. [S1]
- Split at matches: `x = re.split("\s", txt)`. [S1]
- Replace matches: `x = re.sub("\s", "9", txt)`. [S1]
- Match object inspection: `x = re.search(r"\bS\w+", txt); print(x.span()); print(x.group())`. [S1]

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

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 텍스트 검증/추출(이메일 형식 검사 등)에서 표준적으로 쓰이는 도구다. [S1]

## 💻 코드 패턴 (Code patterns)
Match object inspection (Python):
```python
import re
txt = "The rain in Spain"
x = re.search(r"\bS\w+", txt)
print(x.span())   # (12, 18)
print(x.group())  # Spain
```

## ✅ 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 Methods]], [[Python Modules]]
- **참조 맥락:** 패턴 기반 문자열 검색/치환의 표준 도구 — 문자열 메서드로 처리하기 어려운 패턴 매칭에 사용.

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

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