fix: chain exceptions in get_prompt and read_resource handlers#2542
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maxisbey merged 1 commit intomodelcontextprotocol:mainfrom May 8, 2026
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Two raise statements discarded the causal exception chain: - Line 1112: raise ValueError(str(e)) → raise ValueError(str(e)) from e - Line 451: raise ResourceError(...) → raise ResourceError(...) from exc The same file already uses `from exc` correctly at line 459. Without `from`, callers lose the original traceback and cannot programmatically inspect the root cause via __cause__. Fixes modelcontextprotocol#2541
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Summary
Two
raisestatements inserver/mcpserver/server.pydiscard the causal exception chain:raise ValueError(str(e))→raise ValueError(str(e)) from eraise ResourceError(...)→raise ResourceError(...) from excMotivation and Context
The same file uses
from exccorrectly at line 459. These two sites are inconsistent and lose the original traceback, making it impossible for callers to programmatically inspect the root cause via__cause__.Without
from, Python shows "During handling of the above exception, another exception occurred" which is confusing. Withfrom, it shows "The above exception was the direct cause of the following exception" and preserves the chain forisinstance()checks on__cause__.How Has This Been Tested?
The change is purely additive (adds
fromclause) and does not alter control flow or exception types. Existing tests pass unchanged.Fixes #2541