sgl-project/sglang · error · ValueError

Invalid style: {self.sep_style}

Error message

Invalid style: {self.sep_style}

What it means

SeparatorStyle.get_prompt() serializes a conversation according to self.sep_style, and only a fixed set of SeparatorStyle enum members have rendering branches. If a Conversation was constructed with an unrecognized or newly added SeparatorStyle value, the final else branch raises 'Invalid style'.

Source

Thrown at python/sglang/srt/parser/conversation.py:413

                    else:
                        ret += message + self.sep
                else:
                    ret += role + ": "  # must be end with a space
            return ret
        elif self.sep_style == SeparatorStyle.UNLIMITED_OCR:
            seps = [self.sep, self.sep2]
            if system_prompt == "" or system_prompt is None:
                ret = ""
            else:
                ret = system_prompt + seps[0]
            for i, (role, message) in enumerate(self.messages):
                if message:
                    ret += role + message + seps[i % 2]
                else:
                    ret += role
            return ret
        else:
            raise ValueError(f"Invalid style: {self.sep_style}")

    def set_system_message(self, system_message: str):
        """Set the system message."""
        self.system_message = system_message

    def append_message(self, role: str, message: str):
        """Append a new message."""
        self.messages.append([role, message])

    def append_image(self, image: str, detail: Literal["auto", "low", "high"]):
        """Append a new image."""
        self.image_data.append(ImageData(url=image, detail=detail))

    def append_video(self, video: str, preprocess_kwargs: Optional[Dict] = None):
        """Append a new video."""
        if preprocess_kwargs:
            self.video_data.append(
                VideoData(video, preprocess_kwargs=preprocess_kwargs)

View on GitHub (pinned to 0132848349)

Solutions

1. Add a rendering branch in get_prompt() for the missing SeparatorStyle member
2. Verify the sep_style passed to the Conversation constructor is one of the styles handled in get_prompt()
3. Use an existing style (e.g. SeparatorStyle.PLAIN) instead of a custom value

Example fix

# before
conv = Conversation(name="x", sep_style=SeparatorStyle(99), ...)
# after
conv = Conversation(name="x", sep_style=SeparatorStyle.PLAIN, ...)
# or add to get_prompt():
# elif self.sep_style == SeparatorStyle.MY_STYLE: ...

from sglang.srt.parser.conversation import SeparatorStyle
assert conv.sep_style in SeparatorStyle, "unknown sep_style"  # plus ensure get_prompt handles it

When it happens

Trigger: Constructing a Conversation with sep_style set to a SeparatorStyle enum member (or raw int) that has no branch in get_prompt(), e.g. a style added to the enum but not implemented in get_prompt, or a custom/out-of-range integer passed as sep_style.

Common situations: Porting a new chat template into SGLang's conversation.py and registering the enum value without adding a rendering branch; deserializing a Conversation from stale config after an upgrade shifted enum values.

Related errors

• Invalid thinking_mode `{thinking_mode}`
• Unknown role: {role}
• Assistant tool call function.arguments must be valid JSON.
• {template_error}
• {template_error}{suffix}

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/73407b0d5a0663e7. Report an issue: GitHub.