adding pytorch version based on hugging face implementation

pytorch_version.py

@@ -0,0 +1,155 @@
+# From https://github.com/huggingface/pytorch-transformers/blob/master/examples/run_generation.py
+
+import argparse
+import logging
+from tqdm import trange
+
+import torch
+import torch.nn.functional as F
+import numpy as np
+
+from pytorch_transformers import GPT2Config, OpenAIGPTConfig, XLNetConfig, TransfoXLConfig
+
+from pytorch_transformers import GPT2LMHeadModel, GPT2Tokenizer
+from pytorch_transformers import OpenAIGPTLMHeadModel, OpenAIGPTTokenizer
+from pytorch_transformers import XLNetLMHeadModel, XLNetTokenizer
+from pytorch_transformers import TransfoXLLMHeadModel, TransfoXLTokenizer
+
+
+logging.basicConfig(format = '%(asctime)s - %(levelname)s - %(name)s -   %(message)s',
+                    datefmt = '%m/%d/%Y %H:%M:%S',
+                    level = logging.INFO)
+logger = logging.getLogger(__name__)
+
+MAX_LENGTH = int(10000)  # Hardcoded max length to avoid infinite loop
+
+ALL_MODELS = sum((tuple(conf.pretrained_config_archive_map.keys()) for conf in (GPT2Config, OpenAIGPTConfig, XLNetConfig, TransfoXLConfig)), ())
+
+MODEL_CLASSES = {
+    'gpt2': (GPT2LMHeadModel, GPT2Tokenizer),
+    'openai-gpt': (OpenAIGPTLMHeadModel, OpenAIGPTTokenizer),
+    'xlnet': (XLNetLMHeadModel, XLNetTokenizer),
+    'transfo-xl': (TransfoXLLMHeadModel, TransfoXLTokenizer),
+}
+
+# Padding text to help Transformer-XL and XLNet with short prompts as proposed by Aman Rusia
+# in https://github.com/rusiaaman/XLNet-gen#methodology
+# and https://medium.com/@amanrusia/xlnet-speaks-comparison-to-gpt-2-ea1a4e9ba39e
+PADDING_TEXT = """ In 1991, the remains of Russian Tsar Nicholas II and his family
+(except for Alexei and Maria) are discovered.
+The voice of Nicholas's young son, Tsarevich Alexei Nikolaevich, narrates the
+remainder of the story. 1883 Western Siberia,
+a young Grigori Rasputin is asked by his father and a group of men to perform magic.
+Rasputin has a vision and denounces one of the men as a horse thief. Although his
+father initially slaps him for making such an accusation, Rasputin watches as the
+man is chased outside and beaten. Twenty years later, Rasputin sees a vision of
+the Virgin Mary, prompting him to become a priest. Rasputin quickly becomes famous,
+with people, even a bishop, begging for his blessing. <eod> </s> <eos>"""
+
+
+def set_seed(seed, n_gpu=1):
+    np.random.seed(seed)
+    torch.manual_seed(seed)
+    if n_gpu > 0:
+        torch.cuda.manual_seed_all(seed)
+
+
+def top_k_top_p_filtering(logits, top_k=0, top_p=0.0, filter_value=-float('Inf')):
+    """ Filter a distribution of logits using top-k and/or nucleus (top-p) filtering
+        Args:
+            logits: logits distribution shape (vocabulary size)
+            top_k > 0: keep only top k tokens with highest probability (top-k filtering).
+            top_p > 0.0: keep the top tokens with cumulative probability >= top_p (nucleus filtering).
+                Nucleus filtering is described in Holtzman et al. (http://arxiv.org/abs/1904.09751)
+        From: https://gist.github.com/thomwolf/1a5a29f6962089e871b94cbd09daf317
+    """
+    assert logits.dim() == 1  # batch size 1 for now - could be updated for more but the code would be less clear
+    top_k = min(top_k, logits.size(-1))  # Safety check
+    if top_k > 0:
+        # Remove all tokens with a probability less than the last token of the top-k
+        indices_to_remove = logits < torch.topk(logits, top_k)[0][..., -1, None]
+        logits[indices_to_remove] = filter_value
+
+    if top_p > 0.0:
+        sorted_logits, sorted_indices = torch.sort(logits, descending=True)
+        cumulative_probs = torch.cumsum(F.softmax(sorted_logits, dim=-1), dim=-1)
+
+        # Remove tokens with cumulative probability above the threshold
+        sorted_indices_to_remove = cumulative_probs > top_p
+        # Shift the indices to the right to keep also the first token above the threshold
+        sorted_indices_to_remove[..., 1:] = sorted_indices_to_remove[..., :-1].clone()
+        sorted_indices_to_remove[..., 0] = 0
+
+        indices_to_remove = sorted_indices[sorted_indices_to_remove]
+        logits[indices_to_remove] = filter_value
+    return logits
+
+
+def sample_sequence(model, length, context, num_samples=1, temperature=1, top_k=0, top_p=0.0, is_xlnet=False, device='cpu'):
+    context = torch.tensor(context, dtype=torch.long, device=device)
+    context = context.unsqueeze(0).repeat(num_samples, 1)
+    generated = context
+    with torch.no_grad():
+        for _ in trange(length):
+
+            inputs = {'input_ids': generated}
+            if is_xlnet:
+                # XLNet is a direct (predict same token, not next token) and bi-directional model by default
+                # => need one additional dummy token in the input (will be masked), attention mask and target mapping (see model docstring)
+                input_ids = torch.cat((generated, torch.zeros((1, 1), dtype=torch.long, device=device)), dim=1)
+                perm_mask = torch.zeros((1, input_ids.shape[1], input_ids.shape[1]), dtype=torch.float, device=device)
+                perm_mask[:, :, -1] = 1.0  # Previous tokens don't see last token
+                target_mapping = torch.zeros((1, 1, input_ids.shape[1]), dtype=torch.float, device=device)
+                target_mapping[0, 0, -1] = 1.0  # predict last token
+                inputs = {'input_ids': input_ids, 'perm_mask': perm_mask, 'target_mapping': target_mapping}
+
+            outputs = model(**inputs)  # Note: we could also use 'past' with GPT-2/Transfo-XL/XLNet (cached hidden-states)
+            next_token_logits = outputs[0][0, -1, :] / temperature
+            filtered_logits = top_k_top_p_filtering(next_token_logits, top_k=top_k, top_p=top_p)
+            next_token = torch.multinomial(F.softmax(filtered_logits, dim=-1), num_samples=1)
+            generated = torch.cat((generated, next_token.unsqueeze(0)), dim=1)
+    return generated
+
+
+def main():
+
+    device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
+    seed = 150
+    set_seed(seed)
+
+    model_type = "gpt2"
+    model_name = "gpt2-medium"
+    model_class, tokenizer_class = MODEL_CLASSES[model_type]
+    tokenizer = tokenizer_class.from_pretrained(model_name)
+    model = model_class.from_pretrained(model_name)
+    model.to(device)
+    model.eval()
+
+    temperature = 0.9
+    top_k = 40
+    top_p = 1.0
+
+    length = 100
+    while True:
+        raw_text = input("Model prompt >>> ")
+        if model_type in ["transfo-xl", "xlnet"]:
+            # Models with memory likes to have a long prompt for short inputs.
+            raw_text = (PADDING_TEXT) + raw_text
+        context_tokens = tokenizer.encode(raw_text)
+        out = sample_sequence(
+            model=model,
+            context=context_tokens,
+            length=length,
+            temperature=temperature,
+            top_k=top_k,
+            top_p=top_p,
+            device=device,
+            is_xlnet=bool(model_type == "xlnet")
+        )
+        out = out[0, len(context_tokens):].tolist()
+        text = tokenizer.decode(out, clean_up_tokenization_spaces=True)
+        print(text)
+
+
+if __name__ == '__main__':
+    main()