add llama2 chat template (#140)

* add llama2 template

* update readme and fix lint

* update readme

* add bos

* add bos

* remove bos

* Update model.py

---------
Co-authored-by: grimoire <yaoqian@pjlab.org.cn>

README.md

@@ -11,9 +11,10 @@ English | [简体中文](README_zh-CN.md)
 
 ______________________________________________________________________
 
-## News
+## News 🎉
 
-\[2023/07\] TurboMind supports tensor-parallel inference of InternLM.
+- \[2023/07\] TurboMind supports tensor-parallel inference of InternLM.
+- \[2023/07\] TurboMind supports llama2 7b/13b.
 
 ______________________________________________________________________
 

README_zh-CN.md

@@ -11,9 +11,10 @@
 
 ______________________________________________________________________
 
-## 更新
+## 更新 🎉
 
-\[2023/07\] TurboMind 支持 InternLM 的 Tensor Parallel 推理
+- \[2023/07\] TurboMind 支持 InternLM 的 Tensor Parallel 推理
+- \[2023/07\] TurboMind 支持 Llama2 7b/13b 模型
 
 ______________________________________________________________________
 

lmdeploy/model.py

@@ -125,6 +125,50 @@ conversation"""  # noqa: E501
         return [45623]
 
 
+@MODELS.register_module(name='llama2')
+class Llama2:
+    """Chat template of LLaMA2 model."""
+
+    def __init__(self):
+
+        B_INST, E_INST = '[INST]', '[/INST]'
+        B_SYS, E_SYS = '<<SYS>>\n', '\n<</SYS>>\n\n'
+
+        DEFAULT_SYSTEM_PROMPT = """\
+You are a helpful, respectful and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature.
+
+If a question does not make any sense, or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information."""  # noqa: E501
+
+        self.b_inst = B_INST
+        self.e_inst = E_INST
+        self.b_sys = B_SYS
+        self.e_sys = E_SYS
+        self.default_sys_prompt = DEFAULT_SYSTEM_PROMPT
+
+    def get_prompt(self, prompt, sequence_start=True):
+        """Return the prompt that is concatenated with other elements in the
+        chat template.
+
+        Args:
+            prompt (str): user's input prompt
+            sequence_start (bool): indicator for the first round chat of a
+               session sequence
+        Returns:
+            str: the concatenated prompt
+        """
+        if sequence_start:
+            return f'<BOS>{self.b_inst} ' \
+                   f'{self.b_sys} {self.default_sys_prompt} {self.e_sys}' \
+                   f'{prompt} {self.e_inst} '
+
+        return f'{self.b_inst} {prompt} {self.e_inst} '
+
+    @property
+    def stop_words(self):
+        """Return the stop-words' token ids."""
+        return None
+
+
 def main(model_name: str = 'test'):
     assert model_name in MODELS.module_dict.keys(), \
         f"'{model_name}' is not supported. " \