{"record":{"id":"37e92bd9155ae972","repo":"unslothai/unsloth","slug":"no-attempt-rendered-the-continuation-prefix","errorCode":null,"errorMessage":"no attempt rendered the continuation prefix","messagePattern":"no attempt rendered the continuation prefix","errorType":"exception","errorClass":"TypeError","httpStatus":null,"severity":"error","filePath":"studio/backend/core/inference/chat_template_helpers.py","lineNumber":2573,"sourceCode":"        raise RuntimeError(\"apply_chat_template_for_generation: no attempt produced a result\")\n\n    def _render_continuation_manually(msgs: list) -> str:\n        \"\"\"For tokenizers predating ``continue_final_message`` (TypeError above).\n\n        Prefix and partial come from the SAME swept copy: an attempt that drops the tools\n        kwarg re-sweeps for the default template, whose markup would otherwise survive raw.\n        \"\"\"\n        for kwargs in attempts:\n            swept = _swept_for(kwargs, msgs)\n            try:\n                prefix = tokenizer.apply_chat_template(\n                    swept[:-1], tokenize = False, add_generation_prompt = True, **kwargs\n                )\n            except TypeError:\n                continue\n            partial = trailing_assistant_text(swept) or _continue_text\n            return f\"{strip_open_reasoning_prefill(prefix)}{partial}\"\n        raise TypeError(\"no attempt rendered the continuation prefix\")\n\n    def _render_with_fallback(msgs: list) -> str:\n        try:\n            return _render(msgs)\n        except TypeError:\n            if not _continuing:\n                raise\n            return _render_continuation_manually(msgs)\n\n    try:\n        return _render_with_fallback(messages)\n    except Exception:\n        # Retry with repairs applied cumulatively. Originals render first, so\n        # working templates stay byte-identical.\n        candidates: list = []\n        normalized = _normalize_tool_call_arguments(messages)\n        if normalized is not messages:\n            candidates.append(normalized)","sourceCodeStart":2555,"sourceCodeEnd":2591,"githubUrl":"https://github.com/unslothai/unsloth/blob/203007d19051dcd2ae33876786d117c99f6b0368/studio/backend/core/inference/chat_template_helpers.py#L2555-L2591","documentation":"Raised (as TypeError) by _render_continuation_manually when none of the kwarg attempts could even render the prefix (apply_chat_template on swept[:-1] with add_generation_prompt=True). It only runs after the primary _render failed with TypeError while continuing a final assistant message — so the tokenizer cannot render a generation prompt under any swept configuration.","triggerScenarios":"Tokenizer's apply_chat_template always raises TypeError regardless of kwargs (custom subclass, ancient transformers); the swept copy differs from the template's expected input schema (e.g. role/content structure) so every render fails; continue_final_message unsupported AND the manual prefix render also impossible.","commonSituations":"Old transformers without continue_final_message paired with a template that requires it; malformed messages (missing content keys, None values) surviving the sweep; custom tokenizer overriding apply_chat_template.","solutions":["Upgrade transformers to a version supporting continue_final_message so the primary _render path succeeds","Validate the messages list structure (roles/content present, no None) before calling generation","If using a custom tokenizer subclass, ensure apply_chat_template accepts add_generation_prompt and tokenize kwargs"],"exampleFix":null,"handlingStrategy":"try-catch","validationCode":"def messages_renderable(tokenizer, msgs) -> bool:\n    try:\n        tokenizer.apply_chat_template(msgs[:-1], tokenize=False, add_generation_prompt=True)\n        return True\n    except TypeError:\n        return False","typeGuard":null,"tryCatchPattern":"try:\n    prompt = apply_chat_template_for_generation(tokenizer, messages)\nexcept TypeError as e:\n    if \"continuation prefix\" in str(e):\n        upgrade_transformers_hint()\n        prompt = f\"{tokenizer.apply_chat_template(messages[:-1], tokenize=False)}{trailing_text}\"","preventionTips":["Upgrade transformers when using continue_final_message flows","Validate message dict shape before generation","Avoid custom tokenizer subclasses that drop standard apply_chat_template kwargs"],"tags":["chat-template","tokenizer","continuation","transformers"],"backgroundTag":null,"analyzedSha":"203007d19051dcd2ae33876786d117c99f6b0368","analyzedAt":"2026-08-15T02:48:39.846Z","schemaVersion":2},"datasetVersion":"2026-08-15T22:17:37.221Z"}