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# SPDX-FileCopyrightText: 2016-2025 PyThaiNLP Project
# SPDX-FileType: SOURCE
# SPDX-License-Identifier: Apache-2.0
"""
The Royal Thai General System of Transcription (RTGS)
is the official system for rendering Thai words in the Latin alphabet.
It was published by the Royal Institute of Thailand.
:See Also:
* `Wikipedia <https://en.wikipedia.org/wiki/Royal_Thai_General_System_of_Transcription>`_
"""
import re
from pythainlp import thai_consonants, word_tokenize
# vowel
_vowel_patterns = """เ*ียว,\\1iao
แ*็ว,\\1aeo
เ*ือย,\\1ueai
แ*ว,\\1aeo
เ*็ว,\\1eo
เ*ว,\\1eo
*ิว,\\1io
*วย,\\1uai
เ*ย,\\1oei
*อย,\\1oi
โ*ย,\\1oi
*ุย,\\1ui
*าย,\\1ai
ไ*ย,\\1ai
*ัย,\\1ai
ไ**,\\1\\2ai
ไ*,\\1ai
ใ*,\\1ai
*ว*,\\1ua\\2
*ัวะ,\\1ua
*ัว,\\1ua
เ*ือะ,\\1uea
เ*ือ,\\1uea
เ*ียะ,\\1ia
เ*ีย,\\1ia
เ*อะ,\\1oe
เ*อ,\\1oe
เ*ิ,\\1oe
*อ,\\1o
เ*าะ,\\1o
เ*็,\\1e
โ*ะ,\\1o
โ*,\\1o
แ*ะ,\\1ae
แ*,\\1ae
เ*าะ,\\1e
*าว,\\1ao
เ*า,\\1ao
เ*,\\1e
*ู,\\1u
*ุ,\\1u
*ื,\\1ue
*ึ,\\1ue
*ี,\\1i
*ิ,\\1i
*ำ,\\1am
*า,\\1a
*ั,\\1a
*ะ,\\1a
#ฤ,\\1rue
$ฤ,\\1ri"""
_vowel_patterns = _vowel_patterns.replace("*", f"([{thai_consonants}])")
_vowel_patterns = _vowel_patterns.replace("#", "([คนพมห])")
_vowel_patterns = _vowel_patterns.replace("$", "([กตทปศส])")
_VOWELS = [x.split(",") for x in _vowel_patterns.split("\n")]
# พยัญชนะ ต้น สะกด
_CONSONANTS = {
"ก": ["k", "k"],
"ข": ["kh", "k"],
"ฃ": ["kh", "k"],
"ค": ["kh", "k"],
"ฅ": ["kh", "k"],
"ฆ": ["kh", "k"],
"ง": ["ng", "ng"],
"จ": ["ch", "t"],
"ฉ": ["ch", "t"],
"ช": ["ch", "t"],
"ซ": ["s", "t"],
"ฌ": ["ch", "t"],
"ญ": ["y", "n"],
"ฎ": ["d", "t"],
"ฏ": ["t", "t"],
"ฐ": ["th", "t"],
# ฑ พยัญชนะต้น เป็น d ได้
"ฑ": ["th", "t"],
"ฒ": ["th", "t"],
"ณ": ["n", "n"],
"ด": ["d", "t"],
"ต": ["t", "t"],
"ถ": ["th", "t"],
"ท": ["th", "t"],
"ธ": ["th", "t"],
"น": ["n", "n"],
"บ": ["b", "p"],
"ป": ["p", "p"],
"ผ": ["ph", "p"],
"ฝ": ["f", "p"],
"พ": ["ph", "p"],
"ฟ": ["f", "p"],
"ภ": ["ph", "p"],
"ม": ["m", "m"],
"ย": ["y", ""],
"ร": ["r", "n"],
"ฤ": ["rue", ""],
"ล": ["l", "n"],
"ว": ["w", ""],
"ศ": ["s", "t"],
"ษ": ["s", "t"],
"ส": ["s", "t"],
"ห": ["h", ""],
"ฬ": ["l", "n"],
"อ": ["", ""],
"ฮ": ["h", ""],
}
_THANTHAKHAT = "\u0e4c"
_RE_CONSONANT = re.compile(f"[{thai_consonants}]")
_RE_NORMALIZE = re.compile(
f"จน์|มณ์|ณฑ์|ทร์|ตร์|[{thai_consonants}]{_THANTHAKHAT}|"
f"[{thai_consonants}][\u0e30-\u0e39]{_THANTHAKHAT}"
# Paiyannoi, Maiyamok, Tonemarks, Thanthakhat, Nikhahit, other signs
r"|[\u0e2f\u0e46\u0e48-\u0e4f\u0e5a\u0e5b]"
)
def _normalize(word: str) -> str:
"""
Remove silence, no sound, and tonal characters.
ตัดอักษรที่ไม่ออกเสียง (การันต์ ไปยาลน้อย ไม้ยมก*) และวรรณยุกต์ทิ้ง
"""
return _RE_NORMALIZE.sub("", word)
def _replace_vowels(word: str) -> str:
for vowel in _VOWELS:
word = re.sub(vowel[0], vowel[1], word)
return word
def _replace_consonants(word: str, consonants: str) -> str:
_HO_HIP = "\u0e2b" # ห
_RO_RUA = "\u0e23" # ร
_DOUBLE_RO_RUA = _RO_RUA + _RO_RUA
if not consonants:
return word
skip = False
mod_chars = []
j = 0 # j is the index of consonants
for i in range(len(word)):
if skip:
skip = False
j += 1
elif word[i] not in _CONSONANTS: # word[i] is not a Thai consonant.
mod_chars.append(word[i])
elif (
len(mod_chars) == 0 and word[i] == _HO_HIP and len(consonants) != 1
): # Skip HO HIP except that HO HIP is the only one consonant
j += 1
elif (
len(mod_chars) == 0
): # The first character must be an initial consonant.
mod_chars.append(_CONSONANTS[consonants[j]][0])
j += 1
elif word[i:] == _DOUBLE_RO_RUA: # Double RO RUA is in end of word
skip = True
mod_chars.append("a")
mod_chars.append("n")
j += 1
elif word[i : i + 2] == _DOUBLE_RO_RUA:
skip = True
mod_chars.append("a")
j += 1
else: # Assume that the rest are final consonants.
mod_chars.append(_CONSONANTS[consonants[j]][1])
j += 1
return "".join(mod_chars)
# support function for romanize()
def _romanize(word: str) -> str:
word = _replace_vowels(_normalize(word))
consonants = _RE_CONSONANT.findall(word)
# 2-character word, all consonants
if len(word) == 2 and len(consonants) == 2:
word = list(word)
word.insert(1, "o")
word = "".join(word)
word = _replace_consonants(word, consonants)
return word
def romanize(text: str) -> str:
"""Render Thai words in Latin alphabet, using RTGS
Royal Thai General System of Transcription (RTGS),
is the official system by the Royal Institute of Thailand.
:param text: Thai text to be romanized
:type text: str
:return: A string of Thai words rendered in the Latin alphabet
:rtype: str
"""
words = word_tokenize(text)
romanized_words = [_romanize(word) for word in words]
return "".join(romanized_words)
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