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# SPDX-FileCopyrightText: 2016-2025 PyThaiNLP Project
# SPDX-FileType: SOURCE
# SPDX-License-Identifier: Apache-2.0
"""
Thai Grapheme-to-Phoneme (Thai G2P)
GitHub : https://github.com/wannaphong/thai-g2p
"""
import random
import numpy as np
import torch
import torch.nn.functional as F
from torch import nn
from pythainlp.corpus import get_corpus_path
device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
_MODEL_NAME = "thai-g2p"
class ThaiG2P:
"""
Latin transliteration of Thai words, using International Phonetic Alphabet
"""
def __init__(self):
# get the model, download it if it's not available locally
self.__model_filename = get_corpus_path(_MODEL_NAME)
loader = torch.load(self.__model_filename, map_location=device)
INPUT_DIM, E_EMB_DIM, E_HID_DIM, E_DROPOUT = loader["encoder_params"]
OUTPUT_DIM, D_EMB_DIM, D_HID_DIM, D_DROPOUT = loader["decoder_params"]
self._maxlength = 100
self._char_to_ix = loader["char_to_ix"]
self._ix_to_char = loader["ix_to_char"]
self._target_char_to_ix = loader["target_char_to_ix"]
self._ix_to_target_char = loader["ix_to_target_char"]
# encoder/ decoder
# Restore the model and construct the encoder and decoder.
self._encoder = Encoder(INPUT_DIM, E_EMB_DIM, E_HID_DIM, E_DROPOUT)
self._decoder = AttentionDecoder(
OUTPUT_DIM, D_EMB_DIM, D_HID_DIM, D_DROPOUT
)
self._network = Seq2Seq(
self._encoder,
self._decoder,
self._target_char_to_ix["<start>"],
self._target_char_to_ix["<end>"],
self._maxlength,
).to(device)
self._network.load_state_dict(loader["model_state_dict"])
self._network.eval()
def _prepare_sequence_in(self, text: str):
"""
Prepare input sequence for PyTorch.
"""
idxs = []
for ch in text:
if ch in self._char_to_ix:
idxs.append(self._char_to_ix[ch])
else:
idxs.append(self._char_to_ix["<UNK>"])
idxs.append(self._char_to_ix["<end>"])
tensor = torch.tensor(idxs, dtype=torch.long)
return tensor.to(device)
def g2p(self, text: str) -> str:
"""
:param str text: Thai text to be romanized
:return: English (more or less) text that spells out how the Thai text
should be pronounced.
"""
input_tensor = self._prepare_sequence_in(text).view(1, -1)
input_length = [len(text) + 1]
target_tensor_logits = self._network(
input_tensor, input_length, None, 0
)
# Seq2seq model returns <END> as the first token,
# As a result, target_tensor_logits.size() is torch.Size([0])
if target_tensor_logits.size(0) == 0:
target = ["<PAD>"]
else:
target_tensor = (
torch.argmax(target_tensor_logits.squeeze(1), 1)
.cpu()
.detach()
.numpy()
)
target = [self._ix_to_target_char[t] for t in target_tensor]
return "".join(target)
class Encoder(nn.Module):
def __init__(
self, vocabulary_size, embedding_size, hidden_size, dropout=0.5
):
"""Constructor"""
super().__init__()
self.hidden_size = hidden_size
self.character_embedding = nn.Embedding(
vocabulary_size, embedding_size
)
self.rnn = nn.LSTM(
input_size=embedding_size,
hidden_size=hidden_size // 2,
bidirectional=True,
batch_first=True,
)
self.dropout = nn.Dropout(dropout)
def forward(self, sequences, sequences_lengths):
# sequences: (batch_size, sequence_length=MAX_LENGTH)
# sequences_lengths: (batch_size)
batch_size = sequences.size(0)
self.hidden = self.init_hidden(batch_size)
sequences_lengths = np.sort(sequences_lengths)[::-1]
index_sorted = np.argsort(
-sequences_lengths
) # use negation in sort in descending order
index_unsort = np.argsort(index_sorted) # to unsorted sequence
index_sorted = torch.from_numpy(index_sorted)
sequences = sequences.index_select(0, index_sorted.to(device))
sequences = self.character_embedding(sequences)
sequences = self.dropout(sequences)
sequences_packed = nn.utils.rnn.pack_padded_sequence(
sequences, sequences_lengths.copy(), batch_first=True
)
sequences_output, self.hidden = self.rnn(sequences_packed, self.hidden)
sequences_output, _ = nn.utils.rnn.pad_packed_sequence(
sequences_output, batch_first=True
)
index_unsort = torch.from_numpy(index_unsort).to(device)
sequences_output = sequences_output.index_select(
0, index_unsort.clone().detach()
)
return sequences_output, self.hidden
def init_hidden(self, batch_size):
h_0 = torch.zeros(
[2, batch_size, self.hidden_size // 2], requires_grad=True
).to(device)
c_0 = torch.zeros(
[2, batch_size, self.hidden_size // 2], requires_grad=True
).to(device)
return (h_0, c_0)
class Attn(nn.Module):
def __init__(self, method, hidden_size):
super().__init__()
self.method = method
self.hidden_size = hidden_size
if self.method == "general":
self.attn = nn.Linear(self.hidden_size, hidden_size)
elif self.method == "concat":
self.attn = nn.Linear(self.hidden_size * 2, hidden_size)
self.other = nn.Parameter(torch.FloatTensor(1, hidden_size))
def forward(self, hidden, encoder_outputs, mask):
# Calculate energies for each encoder output
if self.method == "dot":
attn_energies = torch.bmm(
encoder_outputs, hidden.transpose(1, 2)
).squeeze(2)
elif self.method == "general":
attn_energies = self.attn(
encoder_outputs.view(-1, encoder_outputs.size(-1))
) # (batch_size * sequence_len, hidden_size)
attn_energies = torch.bmm(
attn_energies.view(*encoder_outputs.size()),
hidden.transpose(1, 2),
).squeeze(
2
) # (batch_size, sequence_len)
elif self.method == "concat":
attn_energies = self.attn(
torch.cat(
(hidden.expand(*encoder_outputs.size()), encoder_outputs),
2,
)
) # (batch_size, sequence_len, hidden_size)
attn_energies = torch.bmm(
attn_energies,
self.other.unsqueeze(0).expand(*hidden.size()).transpose(1, 2),
).squeeze(2)
attn_energies = attn_energies.masked_fill(mask == 0, -1e10)
# Normalize energies to weights in range 0 to 1
return F.softmax(attn_energies, 1)
class AttentionDecoder(nn.Module):
def __init__(
self, vocabulary_size, embedding_size, hidden_size, dropout=0.5
):
"""Constructor"""
super().__init__()
self.vocabulary_size = vocabulary_size
self.hidden_size = hidden_size
self.character_embedding = nn.Embedding(
vocabulary_size, embedding_size
)
self.rnn = nn.LSTM(
input_size=embedding_size + self.hidden_size,
hidden_size=hidden_size,
bidirectional=False,
batch_first=True,
)
self.attn = Attn(method="general", hidden_size=self.hidden_size)
self.linear = nn.Linear(hidden_size, vocabulary_size)
self.dropout = nn.Dropout(dropout)
def forward(self, input_character, last_hidden, encoder_outputs, mask):
""" "Defines the forward computation of the decoder"""
# input_character: (batch_size, 1)
# last_hidden: (batch_size, hidden_dim)
# encoder_outputs: (batch_size, sequence_len, hidden_dim)
# mask: (batch_size, sequence_len)
hidden = last_hidden.permute(1, 0, 2)
attn_weights = self.attn(hidden, encoder_outputs, mask)
context_vector = attn_weights.unsqueeze(1).bmm(encoder_outputs)
context_vector = torch.sum(context_vector, dim=1)
context_vector = context_vector.unsqueeze(1)
embedded = self.character_embedding(input_character)
embedded = self.dropout(embedded)
rnn_input = torch.cat((context_vector, embedded), -1)
output, hidden = self.rnn(rnn_input)
output = output.view(-1, output.size(2))
x = self.linear(output)
return x, hidden[0], attn_weights
class Seq2Seq(nn.Module):
def __init__(
self,
encoder,
decoder,
target_start_token,
target_end_token,
max_length,
):
super().__init__()
self.encoder = encoder
self.decoder = decoder
self.pad_idx = 0
self.target_start_token = target_start_token
self.target_end_token = target_end_token
self.max_length = max_length
assert encoder.hidden_size == decoder.hidden_size
def create_mask(self, source_seq):
mask = source_seq != self.pad_idx
return mask
def forward(
self, source_seq, source_seq_len, target_seq, teacher_forcing_ratio=0.5
):
# source_seq: (batch_size, MAX_LENGTH)
# source_seq_len: (batch_size, 1)
# target_seq: (batch_size, MAX_LENGTH)
batch_size = source_seq.size(0)
start_token = self.target_start_token
end_token = self.target_end_token
max_len = self.max_length
target_vocab_size = self.decoder.vocabulary_size
outputs = torch.zeros(max_len, batch_size, target_vocab_size).to(
device
)
if target_seq is None:
assert teacher_forcing_ratio == 0, "Must be zero during inference"
inference = True
else:
inference = False
encoder_outputs, encoder_hidden = self.encoder(
source_seq, source_seq_len
)
decoder_input = (
torch.tensor([[start_token] * batch_size])
.view(batch_size, 1)
.to(device)
)
encoder_hidden_h_t = torch.cat(
[encoder_hidden[0][0], encoder_hidden[0][1]], dim=1
).unsqueeze(dim=0)
decoder_hidden = encoder_hidden_h_t
max_source_len = encoder_outputs.size(1)
mask = self.create_mask(source_seq[:, 0:max_source_len])
for di in range(max_len):
decoder_output, decoder_hidden, _ = self.decoder(
decoder_input, decoder_hidden, encoder_outputs, mask
)
_, topi = decoder_output.topk(1)
outputs[di] = decoder_output.to(device)
teacher_force = random.random() < teacher_forcing_ratio
decoder_input = (
target_seq[:, di].reshape(batch_size, 1)
if teacher_force
else topi.detach()
)
if inference and decoder_input == end_token:
return outputs[:di]
return outputs
_THAI_G2P = ThaiG2P()
def transliterate(text: str) -> str:
return _THAI_G2P.g2p(text)
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