Fix #355: Fix type error with lifespan context #368
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The TypeVar LifespanContextT was incorrectly defined with a default=None, which caused type errors when using strongly typed custom context objects. This change properly propagates the type information from custom lifespans to request contexts.
Kludex
reviewed
Mar 25, 2025
| @@ -7,7 +7,7 @@ | |||
| from mcp.types import RequestId, RequestParams | |||
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| SessionT = TypeVar("SessionT", bound=BaseSession[Any, Any, Any, Any, Any]) | |||
| LifespanContextT = TypeVar("LifespanContextT", default=None) | |||
| LifespanContextT = TypeVar("LifespanContextT") | |||
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But doesn't it makes sense to default to None on FastMCP context?
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FastMCP sets the default lifespan which yields and empty dictionary. There is actually never a None. This one defaults to Any, if default is not set, which I think is correct.
Kludex
approved these changes
Mar 25, 2025
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This PR doesn't fix the typing tho |
I am confused, it very much fixes the issue for me |
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🤔 
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Summary
Fix type error when using strongly typed custom lifespan contexts with FastMCP.