app.py

import streamlit as st
import torch
import torch.nn as nn
from torch.nn import functional as F
import pickle
import os

st.title('LLM from scratch Demo')

device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
block_size = 128
batch_size = 32
max_iters = 4000
learning_rate = 3e-4
eval_every = 500
n_embd = 384
n_head = 8
n_layer = 8
dropout = 0.2


class Head(nn.Module):
    """ one head of self-attention """

    def __init__(self, head_size):
        super().__init__()
        self.key = nn.Linear(n_embd, head_size, bias=False)
        self.query = nn.Linear(n_embd, head_size, bias=False)
        self.value = nn.Linear(n_embd, head_size, bias=False)
        self.register_buffer('tril', torch.tril(torch.ones(block_size, block_size)))

        self.dropout = nn.Dropout(dropout)

    def forward(self, x):
        # input of size (batch, time-step, channels)
        # output of size (batch, time-step, head size)
        B,T,C = x.shape
        k = self.key(x)   # (B,T,hs)
        q = self.query(x) # (B,T,hs)
        # compute attention scores ("affinities")
        wei = q @ k.transpose(-2,-1) * k.shape[-1]**-0.5 # (B, T, hs) @ (B, hs, T) -> (B, T, T)
        wei = wei.masked_fill(self.tril[:T, :T] == 0, float('-inf')) # (B, T, T)
        wei = F.softmax(wei, dim=-1) # (B, T, T)
        wei = self.dropout(wei)
        # perform the weighted aggregation of the values
        v = self.value(x) # (B,T,hs)
        out = wei @ v # (B, T, T) @ (B, T, hs) -> (B, T, hs)
        return out

class MultiHeadAttention(nn.Module):
    """ multiple heads of self-attention in parallel """

    def __init__(self, num_heads, head_size):
        super().__init__()
        self.heads = nn.ModuleList([Head(head_size) for _ in range(num_heads)])
        self.proj = nn.Linear(head_size * num_heads, n_embd)
        self.dropout = nn.Dropout(dropout)

    def forward(self, x):
        out = torch.cat([h(x) for h in self.heads], dim=-1) # (B, T, F) -> (B, T, [h1, h1, h1, h1, h2, h2, h2, h2, h3, h3, h3, h3])
        out = self.dropout(self.proj(out))
        return out
    
class FeedFoward(nn.Module):
    """ a simple linear layer followed by a non-linearity """

    def __init__(self, n_embd):
        super().__init__()
        self.net = nn.Sequential(
            nn.Linear(n_embd, 4 * n_embd),
            nn.ReLU(),
            nn.Linear(4 * n_embd, n_embd),
            nn.Dropout(dropout),
        )

    def forward(self, x):
        return self.net(x)
    
class Block(nn.Module):
    """ Transformer block: communication followed by computation """

    def __init__(self, n_embd, n_head):
        # n_embd: embedding dimension, n_head: the number of heads we'd like
        super().__init__()
        head_size = n_embd // n_head
        self.sa = MultiHeadAttention(n_head, head_size)
        self.ffwd = FeedFoward(n_embd)
        self.ln1 = nn.LayerNorm(n_embd)
        self.ln2 = nn.LayerNorm(n_embd)

    def forward(self, x):
        y = self.sa(x)
        x = self.ln1(x + y)
        y = self.ffwd(x)
        x = self.ln2(x + y)
        return x
    
class GPTLanguageModel(nn.Module):
    def __init__(self, vocab_size):
        super().__init__()
        self.token_embedding_table = nn.Embedding(vocab_size, n_embd)
        self.position_embedding_table = nn.Embedding(block_size, n_embd)
        self.blocks = nn.Sequential(*[Block(n_embd, n_head=n_head) for _ in range(n_layer)])
        self.ln_f = nn.LayerNorm(n_embd) # final layer norm
        self.lm_head = nn.Linear(n_embd, vocab_size)
        
        
        self.apply(self._init_weights)

    def _init_weights(self, module):
        if isinstance(module, nn.Linear):
            torch.nn.init.normal_(module.weight, mean=0.0, std=0.02)
            if module.bias is not None:
                torch.nn.init.zeros_(module.bias)
        elif isinstance(module, nn.Embedding):
            torch.nn.init.normal_(module.weight, mean=0.0, std=0.02)

    def forward(self, index, targets=None):
        B, T = index.shape
        
        
        # idx and targets are both (B,T) tensor of integers
        tok_emb = self.token_embedding_table(index) # (B,T,C)
        pos_emb = self.position_embedding_table(torch.arange(T, device=device)) # (T,C)
        x = tok_emb + pos_emb # (B,T,C)
        x = self.blocks(x) # (B,T,C)
        x = self.ln_f(x) # (B,T,C)
        logits = self.lm_head(x) # (B,T,vocab_size)
        
        if targets is None:
            loss = None
        else:
            B, T, C = logits.shape
            logits = logits.view(B*T, C) # reshape to what torch.cross_entropy expects
            targets = targets.view(B*T)
            loss = F.cross_entropy(logits, targets) 
        return logits, loss
    
    def generate(self, index, max_new_tokens):
        # index is (B, T) array of indices in the current context
        for _ in range(max_new_tokens):
            # crop idx to the last block_size tokens
            index_cond = index[:, -block_size:]
            # get the predictions
            logits, loss = self.forward(index_cond)
            # focus only on the last time step
            logits = logits[:, -1, :] # becomes (B, C)
            # apply softmax to get probabilities
            probs = F.softmax(logits, dim=-1) # (B, C)
            # sample from the distribution
            index_next = torch.multinomial(probs, num_samples=1) # (B, 1)
            # append sampled index to the running sequence
            index = torch.cat((index, index_next), dim=1) # (B, T+1)
        return index

if not os.path.exists("./vocab.txt"):
    raise Exception("Please run extract.py first")
chars = ""
with open("./vocab.txt", 'r', encoding='utf-8') as f:
    text = f.read()
    chars = sorted(list(set(text)))

string_to_int = {ch: i for i, ch in enumerate(chars)}
int_to_string = {i: ch for i, ch in enumerate(chars)}

encode = lambda s: [string_to_int[ch] for ch in s]
decode = lambda x: ''.join([int_to_string[i] for i in x])


model_pickle_path = './model.pkl'

try:
    st.write('loading model parameters...')
    with open(model_pickle_path, 'rb') as f:
        model = pickle.load(f)
    st.write('model loaded successfully!')
except:
    st.error('ERROR: model loading failed/model not found. Please run ./train_gpt_openwebtext.py first.')
    exit()

prompt = ''
prompt = st.text_area('Prompt:', value=prompt, height=100, max_chars=block_size - 1, key='prompt')
if len(prompt) != 0:
    context = torch.tensor(encode(prompt), dtype=torch.long, device=device)
    max_new_tokens = block_size - len(prompt)
    generated_chars = decode(model.generate(context.unsqueeze(0), max_new_tokens=max_new_tokens)[0].tolist())
    st.write('Generated text:')
    st.write(generated_chars)