{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# GPT2 LM"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<div class=\"alert alert-info\">\n",
    "\n",
    "This tutorial is available as an IPython notebook at [malaya-speech/example/gpt2-lm](https://github.com/huseinzol05/malaya-speech/tree/master/example/gpt2-lm).\n",
    "    \n",
    "</div>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<div class=\"alert alert-warning\">\n",
    "\n",
    "This module is not language independent, so it not save to use on different languages. Pretrained models trained on hyperlocal languages.\n",
    "    \n",
    "</div>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Purpose"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "When doing CTC or RNNT beam decoding, we want to add language bias during find the optimum alignment using GPT2 Causal model."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### List available GPT2\n",
    "\n",
    "We provided a few GPT2 models for our ASR models,"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import malaya_speech"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
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       "      <th></th>\n",
       "      <th>Size (MB)</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>mesolitica/gpt2-117m-bahasa-cased</th>\n",
       "      <td>454</td>\n",
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       "                                   Size (MB)\n",
       "mesolitica/gpt2-117m-bahasa-cased        454"
      ]
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     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "malaya_speech.language_model.available_gpt2()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Load KenLM Model\n",
    "\n",
    "```python\n",
    "def gpt2(model: str = 'mesolitica/gpt2-117m-bahasa-cased', force_check: bool = True, **kwargs):\n",
    "    \"\"\"\n",
    "    Load GPT2 language model.\n",
    "\n",
    "    Parameters\n",
    "    ----------\n",
    "    model: str, optional (default='mesolitica/gpt2-117m-bahasa-cased')\n",
    "        Check available models at `malaya_speech.language_model.available_gpt2()`.\n",
    "    force_check: bool, optional (default=True)\n",
    "        Force check model one of malaya model.\n",
    "        Set to False if you have your own huggingface model.\n",
    "\n",
    "    Returns\n",
    "    -------\n",
    "    result: malaya.torch_model.gpt2_lm.LM class\n",
    "    \"\"\"\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<malaya_speech.torch_model.gpt2_lm.LM at 0x7f9ca3419f70>"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "lm = malaya_speech.language_model.gpt2()\n",
    "lm"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "malaya-speech GPT2 LM need to combine with `pyctcdecode` to decode CTC logits."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Use pyctcdecode\n",
    "\n",
    "#### From PYPI\n",
    "\n",
    "```bash\n",
    "pip3 install pyctcdecode==0.1.0 pypi-kenlm==0.1.20210121\n",
    "```\n",
    "\n",
    "#### From source\n",
    "\n",
    "Check https://github.com/kensho-technologies/pyctcdecode how to build from source incase there is no available wheel for your operating system.\n",
    "\n",
    "Building from source should only take a few minutes."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "from pyctcdecode import Alphabet, BeamSearchDecoderCTC\n",
    "from malaya_speech.utils.char import CTC_VOCAB\n",
    "\n",
    "labels = CTC_VOCAB + ['_']\n",
    "ctc_token_idx = len(CTC_VOCAB)\n",
    "alphabet = Alphabet.build_alphabet(labels, ctc_token_idx=ctc_token_idx)\n",
    "decoder = BeamSearchDecoderCTC(alphabet, lm)"
   ]
  }
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