Biểu thức chính quy Unicode

What Are Unicode Regular Expressions?

Unicode regular expressions extend the classical regular expression model to handle Unicode text correctly. The key feature is Unicode property escapes — assertions that match characters based on their Unicode properties rather than specific character ranges.

The most important syntax is \p{Property} (matches characters with the given property) and \P{Property} (matches characters without it). A complementary syntax \p{Property=Value} matches specific property values.

JavaScript Unicode Property Escapes (ES2018)

JavaScript's u flag enables Unicode mode; the v flag (ES2024) adds set notation:

// Script property
/\p{Script=Latin}/u.test("a")       // true
/\p{Script=Han}/u.test("中")         // true
/\p{Script=Hiragana}/u.test("あ")   // true

// General Category
/\p{Letter}/u.test("a")             // true
/\p{Decimal_Number}/u.test("5")     // true
/\p{Emoji}/u.test("😀")             // true

// Derived properties
/\p{Lowercase_Letter}/u.test("a")   // true
/\p{Uppercase_Letter}/u.test("A")   // true

// Matching all CJK characters
const cjkPattern = /\p{Script=Han}+/u;
cjkPattern.exec("Hello 世界!")       // ["世界"]

// Negation
/\P{ASCII}/u.test("café")           // true (é is non-ASCII)

// Named Unicode blocks (v flag)
/[\p{Script=Greek}&&\p{Lowercase_Letter}]/v.test("α")  // true

Python Unicode Regex (regex module)

Python's built-in re module has limited Unicode support. The third-party regex module provides full Unicode property support:

import regex  # pip install regex

# Match Unicode letters (any script)
regex.findall(r"\p{L}+", "Hello, 世界, مرحبا")
# ["Hello", "世界", "مرحبا"]

# Match Unicode digits (includes Arabic-Indic, etc.)
regex.findall(r"\p{Nd}+", "Price: ١٢٣ or 123")
# ["١٢٣", "123"]

# Script-specific
regex.findall(r"\p{Script=Arabic}", "مرحبا Hello")
# ["م", "ر", "ح", "ب", "ا"]

# Category: punctuation
regex.findall(r"\p{P}+", "Hello, world! How's it?")
# [",", "!", "'", "?"]

# Standard re: only basic Unicode support
import re
re.findall(r"\w+", "Hello, 世界", flags=re.UNICODE)
# ["Hello", "世界"]  — \w matches Unicode letters with re.UNICODE

Key Unicode Properties for Regex

Practical Validation Examples

// Validate that a username contains only letters, digits, underscores
// Works for all scripts, not just ASCII
function isValidUsername(name) {
  return /^[\p{L}\p{N}_]{3,30}$/u.test(name);
}

isValidUsername("user_123")    // true
isValidUsername("用户名")       // true (Chinese letters)
isValidUsername("<script>")    // false

// Extract hashtags including non-Latin
function extractHashtags(text) {
  return [...text.matchAll(/#\p{L}[\p{L}\p{N}]*/gu)].map(m => m[0]);
}

extractHashtags("Check #Unicode and #유니코드!")
// ["#Unicode", "#유니코드"]

Grapheme Cluster Matching

The \X pattern in the regex module matches a full grapheme cluster:

import regex

# \X matches one grapheme (not one code point)
regex.findall(r"\X", "café")          # ["c", "a", "f", "é"]  (4 graphemes)
regex.findall(r"\X", "👨‍👩‍👧")      # ["👨‍👩‍👧"]  (1 grapheme)
regex.findall(r"\X", "🇺🇸 flag")    # ["🇺🇸", " ", "f", "l", "a", "g"]

Quick Facts