Unicode 字符数据库 (UCD)

What is the Unicode Character Database?

The Unicode Character Database (UCD) is the authoritative, machine-readable repository of all properties for every Unicode code point. Where the Unicode Standard describes characters in prose and tables, the UCD provides that same information in structured data files that software libraries can parse and implement automatically. Every Unicode library — ICU, Python's unicodedata, Java's Character class, .NET's CharUnicodeInfo — is built from the UCD.

The UCD is distributed as a collection of plain-text files published on unicode.org for each Unicode version. The files follow documented formats (simple tables, two-column mappings, or the comprehensive UnicodeData.txt) and are freely available for any use.

Core UCD Files

UnicodeData.txt Format

The most important UCD file is UnicodeData.txt. Each line has 15 semicolon-delimited fields:

0041;LATIN CAPITAL LETTER A;Lu;0;L;;;;;N;;;;0061;
│    │                       │  │ │
│    │                       │  │ └── Bidi class (L = Left-to-right)
│    │                       │  └──── Canonical combining class (0 = not combining)
│    │                       └─────── General category (Lu = Uppercase Letter)
│    └─────────────────────────────── Character name
└──────────────────────────────────── Code point (hex)

The 15 fields in order: 1. Code point (hex) 2. Character name 3. General category 4. Canonical combining class 5. Bidi class 6. Character decomposition 7–9. Numeric values (decimal, digit, numeric) 10. Mirror flag 11. Unicode 1.0 name (legacy) 12. ISO comment (deprecated) 13–15. Uppercase, lowercase, titlecase mappings

Using the UCD in Practice

import unicodedata

# Python's unicodedata module is a UCD interface
char = "A"
print(unicodedata.name(char))           # LATIN CAPITAL LETTER A
print(unicodedata.category(char))       # Lu (Uppercase Letter)
print(unicodedata.bidirectional(char))  # L
print(unicodedata.combining(char))      # 0 (non-combining)
print(unicodedata.normalize("NFD", "é")) # e + combining accent

# Reading UnicodeData.txt directly
import urllib.request

url = "https://unicode.org/Public/UCD/latest/ucd/UnicodeData.txt"
with urllib.request.urlopen(url) as f:
    for line in f:
        fields = line.decode().strip().split(";")
        cp, name, category = fields[0], fields[1], fields[2]
        if category == "So":  # Other Symbol
            print(f"U+{cp}: {name}")

Common Pitfalls

Name vs Alias: UnicodeData.txt lists the normative name, but some characters have aliases (corrections to historical naming errors). For example, U+FE18 is officially named PRESENTATION FORM FOR VERTICAL RIGHT WHITE LENTICULAR BRAKCET (note the typo), but the alias file provides the corrected name.

Ranges in UnicodeData.txt: CJK Unified Ideographs are not listed individually. Instead, two lines mark the start and end of the range:

4E00;<CJK Ideograph, First>;Lo;0;L;;;;;N;;;;;
9FFF;<CJK Ideograph, Last>;Lo;0;L;;;;;N;;;;;

Quick Facts