re 에 관해서

🧠 Python re Module — Summary

🔧 Commonly Used Methods:

Method	Description	Example
re.search()	Finds the first match anywhere in the string	re.search(r'\d+', 'abc123') → '123'
re.match()	Matches a pattern only at the beginning	re.match(r'\d+', '123abc') → '123'
re.findall()	Returns all non-overlapping matches as a list	re.findall(r'\d+', 'a1b22') → ['1', '22']
re.sub()	Replaces matched substrings	re.sub(r'\d+', '*', 'abc123') → 'abc*'
re.split()	Splits string based on regex pattern	re.split(r'[\s,]+', 'a, b c') → ['a', 'b', 'c']

Use r'...' to write regex in Python so that backslashes like \s are treated literally, not as Python escape characters. ✅

📘 Regex Pattern Cheatsheet:

Pattern	Meaning	Example Match
\d	Digit (0–9)	'1', '5'
\D	Non-digit	'a', '#'
\w	Word character (a-z, A-Z, 0–9, _)	'a', 'Z', '7'
\W	Non-word character	'@', ' '
\s	Whitespace (space, tab, newline)	' ', '\n', '\t'
\S	Non-whitespace	'a', '1', '.'
.	Any character (except newline)	'a', '5', '!'
*	0 or more times	'a*' → '', 'aaa'
+	1 or more times	'a+' → 'a', 'aa'
{m,n}	Between m and n times	'a{2,4}' → 'aa'
`	`	OR
()	Grouping	(\d+)-(\w+)
[]	Character set	[a-z], [0-9]

---

✅ Examples we've used:

command = "G()(al)"

1. Replace () with "o" and (al) with "al":

re.sub(r'\(\)', 'o', re.sub(r'\(al\)', 'al', command))

2. Extract all numbers:

re.findall(r'\d+', 'I have 2 apples and 10 bananas')  # ['2', '10']

3. Replace multiple spaces with one:

re.sub(r'\s+', ' ', 'This   is  ChatGPT')  # 'This is ChatGPT'

4. Split by space, comma, or semicolon:

re.split(r'[,\s;]+', 'apple, banana; orange')  # ['apple', 'banana', 'orange']

---

🧪 Example 1: Check if a string is a valid email

import re

email = "test123@example.com"
if re.match(r'^[\w\.-]+@[\w\.-]+\.\w+$', email):
    print("✅ Valid email")
else:
    print("❌ Invalid email")

🧪 Example 2: Extract all words that start with a capital letter

text = "Alice and Bob went to NewYork"
capital_words = re.findall(r'\b[A-Z][a-z]*\b', text)
print(capital_words)  # ['Alice', 'Bob', 'NewYork']

🧪 Example 3: Replace all digits with #

text = "My phone number is 010-1234-5678"
masked = re.sub(r'\d', '#', text)
print(masked)  # "My phone number is ###-####-####"

🧪 Example 4: Extract hashtags from a sentence

text = "Today is great! #sunny #happy #blessed"
hashtags = re.findall(r'#\w+', text)
print(hashtags)  # ['#sunny', '#happy', '#blessed']

🧪 Example 5: Remove HTML tags

html = "<div>Hello <b>world</b></div>"
cleaned = re.sub(r'<.*?>', '', html)
print(cleaned)  # "Hello world"