Refactor ChatTemplate for Enhanced Clarity and Efficiency (#201)

python/sglang/lang/chat_template.py

@@ -12,42 +12,35 @@ class ChatTemplateStyle(Enum):
 class ChatTemplate:
     name: str
     default_system_prompt: str
-    role_prefix_and_suffix: Dict[str, Tuple[str]]
+    role_prefix_and_suffix: Dict[str, Tuple[str, str]]
     stop_str: List[str] = ()
     image_token: str = "<image>"
     style: ChatTemplateStyle = ChatTemplateStyle.PLAIN
 
-    def get_prefix_and_suffix(self, role, hist_messages):
-        if self.style == ChatTemplateStyle.PLAIN:
-            return self.role_prefix_and_suffix[role]
-        elif self.style == ChatTemplateStyle.LLAMA2:
-            if len(hist_messages) == 0 and role == "system":
-                return (
-                    self.role_prefix_and_suffix["user"][0]
-                    + self.role_prefix_and_suffix["system"][0],
-                    self.role_prefix_and_suffix["system"][1],
-                )
-            elif (
-                len(hist_messages) == 1
-                and role == "user"
-                and hist_messages[0]["content"] is not None
-            ):
-                return ("", self.role_prefix_and_suffix["user"][1])
-            return self.role_prefix_and_suffix[role]
-        else:
-            raise ValueError(f"Invalid style: {self.style}")
+    def get_prefix_and_suffix(self, role: str, hist_messages: List[Dict]) -> Tuple[str, str]:
+        prefix, suffix = self.role_prefix_and_suffix.get(role, ("", ""))
+        
+        if self.style == ChatTemplateStyle.LLAMA2:
+            if role == "system" and not hist_messages:
+                user_prefix, _ = self.role_prefix_and_suffix.get("user", ("", ""))
+                system_prefix, system_suffix = self.role_prefix_and_suffix.get("system", ("", ""))
+                return (user_prefix + system_prefix, system_suffix)
+            elif role == "user" and len(hist_messages) == 1 and hist_messages[0]["content"] is not None:
+                return ("", suffix)
 
-    def get_prompt(self, messages):
+        return prefix, suffix
+
+    def get_prompt(self, messages: List[Dict]) -> str:
         prompt = ""
-        for i in range(len(messages)):
-            role, content = messages[i]["role"], messages[i]["content"]
+        for i, message in enumerate(messages):
+            role, content = message["role"], message["content"]
             if role == "system" and content is None:
                 content = self.default_system_prompt
                 if content is None:
                     continue
 
             prefix, suffix = self.get_prefix_and_suffix(role, messages[:i])
-            prompt += prefix + content + suffix
+            prompt += f"{prefix}{content}{suffix}"
         return prompt