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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"raise ValueError(str(e)) discards exception chain in get_prompt handler","articleBody":"### Initial Checks\n\n- [x] I confirm that I'm using the latest version of MCP Python SDK\n- [x] I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue\n\n### Description\n\nIn `server/mcpserver/server.py`, the `get_prompt` handler catches all exceptions and re-raises as `ValueError(str(e))` without chaining:\n\n**Line 1110-1112:**\n```python\nexcept Exception as e:\n    logger.exception(f\"Error getting prompt {name}\")\n    raise ValueError(str(e))\n```\n\nThis discards the original exception's type, traceback, and identity. Callers cannot use `isinstance()` or `__cause__` to determine what went wrong.\n\nThe same file uses the correct pattern eight lines earlier (line 459):\n```python\nraise ResourceError(f\"Error reading resource {uri}\") from exc\n```\n\nA second instance at line 451 also omits `from`:\n```python\nexcept ValueError:\n    raise ResourceError(f\"Unknown resource: {uri}\")\n```\n\n### Fix\n\n```python\n# Line 1112\nraise ValueError(str(e)) from e\n\n# Line 451\nexcept ValueError as exc:\n    raise ResourceError(f\"Unknown resource: {uri}\") from exc\n```\n\n### Impact\n\nWithout `from`, Python shows \"During handling of the above exception, another exception occurred\" which is confusing. With `from`, it shows \"The above exception was the direct cause of the following exception\" and preserves `__cause__` for programmatic inspection.","author":{"url":"https://github.com/blackwell-systems","@type":"Person","name":"blackwell-systems"},"datePublished":"2026-05-05T01:52:12.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/2541/python-sdk/issues/2541"}