app.py

import torch
import joblib

import numpy as np
import pandas as pd
import gradio as gr

from nltk.data import load as nltk_load
from transformers import AutoTokenizer, AutoModelForCausalLM


print("Loading model & Tokenizer...")
model_id  = 'gpt2-large'
tokenizer = AutoTokenizer.from_pretrained(model_id)
model     = AutoModelForCausalLM.from_pretrained(model_id)

print("Loading NLTL & and scikit-learn model...")
NLTK = nltk_load('data/english.pickle')
sent_cut_en = NLTK.tokenize
clf = joblib.load(f'data/gpt2-large-model', 'rb')

CROSS_ENTROPY = torch.nn.CrossEntropyLoss(reduction='none')


def gpt2_features(text, tokenizer, model, sent_cut):
    # Tokenize
    input_max_length = tokenizer.model_max_length - 2
    token_ids, offsets = list(), list()
    sentences = sent_cut(text)
    for s in sentences:
        tokens = tokenizer.tokenize(s)
        ids = tokenizer.convert_tokens_to_ids(tokens)
        difference = len(token_ids) + len(ids) - input_max_length
        if difference > 0:
            ids = ids[:-difference]
        offsets.append((len(token_ids), len(token_ids) + len(ids)))
        token_ids.extend(ids)
        if difference >= 0:
            break

    input_ids = torch.tensor([tokenizer.bos_token_id] + token_ids)
    logits = model(input_ids).logits
    # Shift so that n-1 predict n
    shift_logits = logits[:-1].contiguous()
    shift_target = input_ids[1:].contiguous()
    loss = CROSS_ENTROPY(shift_logits, shift_target)

    all_probs = torch.softmax(shift_logits, dim=-1)
    sorted_ids = torch.argsort(all_probs, dim=-1, descending=True)  # stable=True
    expanded_tokens = shift_target.unsqueeze(-1).expand_as(sorted_ids)
    indices = torch.where(sorted_ids == expanded_tokens)
    rank = indices[-1]
    counter = [
        rank < 10,
        (rank >= 10) & (rank < 100),
        (rank >= 100) & (rank < 1000),
        rank >= 1000
    ]
    counter = [c.long().sum(-1).item() for c in counter]


    # compute different-level ppl
    text_ppl = loss.mean().exp().item()
    sent_ppl = list()
    for start, end in offsets:
        nll = loss[start: end].sum() / (end - start)
        sent_ppl.append(nll.exp().item())
    max_sent_ppl = max(sent_ppl)
    sent_ppl_avg = sum(sent_ppl) / len(sent_ppl)
    if len(sent_ppl) > 1:
        sent_ppl_std = torch.std(torch.tensor(sent_ppl)).item()
    else:
        sent_ppl_std = 0

    mask = torch.tensor([1] * loss.size(0))
    step_ppl = loss.cumsum(dim=-1).div(mask.cumsum(dim=-1)).exp()
    max_step_ppl = step_ppl.max(dim=-1)[0].item()
    step_ppl_avg = step_ppl.sum(dim=-1).div(loss.size(0)).item()
    if step_ppl.size(0) > 1:
        step_ppl_std = step_ppl.std().item()
    else:
        step_ppl_std = 0
    ppls = [
        text_ppl, max_sent_ppl, sent_ppl_avg, sent_ppl_std,
        max_step_ppl, step_ppl_avg, step_ppl_std
    ]
    return ppls + counter  # type: ignore


def predict(features, classifier, id_to_label):
    x = np.asarray([features])
    pred = classifier.predict(x)[0]
    prob = classifier.predict_proba(x)[0, pred]
    return [id_to_label[pred], prob]


def predict(text):
    with torch.no_grad():
        feats = gpt2_features(text, tokenizer, model, sent_cut_en)
    out = predict(*feats, clf, ['Human Written', 'LLM Generated'])
    return out


print("Building Gradio Interface...")
with gr.Blocks() as demo:
    gr.Markdown(
        """
        ## ChatGPT Detector 🔬 (Linguistic version / 语言学版)

        Visit our project on Github: [chatgpt-comparison-detection project](https://github.com/Hello-SimpleAI/chatgpt-comparison-detection)<br>
        欢迎在 Github 上关注我们的 [ChatGPT 对比与检测项目](https://github.com/Hello-SimpleAI/chatgpt-comparison-detection)<br>
        We provide three kinds of detectors, all in Bilingual / 我们提供了三个版本的检测器，且都支持中英文:
        - [QA version / 问答版](https://www.modelscope.cn/studios/simpleai/chatgpt-detector-qa)<br>
            detect whether an **answer** is generated by ChatGPT for certain **question**, using PLM-based classifiers / 判断某个**问题的回答**是否由ChatGPT生成，使用基于PTM的分类器来开发;
        - [Sinlge-text version / 独立文本版](https://www.modelscope.cn/studios/simpleai/chatgpt-detector-single)<br>
            detect whether a piece of text is ChatGPT generated, using PLM-based classifiers / 判断**单条文本**是否由ChatGPT生成，使用基于PTM的分类器来开发;
        - [**Linguistic version / 语言学版** (👈 Current / 当前使用)](https://www.modelscope.cn/studios/simpleai/chatgpt-detector-ling)<br>
            detect whether a piece of text is ChatGPT generated, using linguistic features / 判断**单条文本**是否由ChatGPT生成，使用基于语言学特征的模型来开发;

        """
    )

    gr.Markdown(
        """
        ## Introduction:
        Two Logistic regression models trained with two kinds of features:
        1. [GLTR](https://aclanthology.org/P19-3019) Test-2, Language model predict token rank top-k buckets, top 10, 10-100, 100-1000, 1000+.
        2. PPL-based, text ppl, sentence ppl, etc.

        English LM is [GPT2-small](https://huggingface.co/gpt2).

        Note: Providing more text to the `Text` box can make the prediction more accurate!
        """
    )
    a1 = gr.Textbox(
        lines=5, label='Text',
        value="There are a few things that can help protect your credit card information from being misused when you give it to a restaurant or any other business:\n\nEncryption: Many businesses use encryption to protect your credit card information when it is being transmitted or stored. This means that the information is transformed into a code that is difficult for anyone to read without the right key."
    )
    button1 = gr.Button("🤖 Predict!")
    gr.Markdown("GLTR")
    label1_gltr = gr.Textbox(lines=1, label='GLTR Predicted Label 🎃')
    score1_gltr = gr.Textbox(lines=1, label='GLTR Probability')

    button1.click(predict, inputs=[a1], outputs=[label1_gltr, score1_gltr])

demo.launch()