Improve Runnable type inference for input_schemas #12630
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nfcampos
commented
Oct 31, 2023
•
nfcampos
commented
- Prefer lambda type annotations over inferred dict schema
- For sequences that start with RunnableAssign infer seq input type as "input type of 2nd item in sequence - output type of runnable assign"
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…t type of 2nd item in sequence - output type of runnable assign"
| from langchain.schema.runnable.passthrough import RunnableAssign | ||
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| if isinstance(self.first, RunnableAssign): | ||
| first = cast(RunnableAssign, self.first) |
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mypy supports type narrowing, which makes the cast here a no-op. Narrowing here means that it sees that it's inside an if whose condition ensures self.first's type is RunnableAssign, and for the rest of the block it knows that self.first stays RunnableAssign even though outside the block it could be something else.
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For some reason mypy was inferring this here as Never. Maybe because this is a bit circular (thus the import inside the function)
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Huh, that's wild. Sounds like a bug.
Never might have been appropriate if Runnable and RunnableAssign didn't have any classes in common (i.e. could not both be true), but RunnableAssign is a Runnable already.
We're unfortunately running a year-old version of mypy (0.9xx instead of 1.6.1 which is latest) so I don't think we can report this or get help on it until we upgrade. It's possible that upgrading gets us bug fixes for stuff like this.
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Might also be good to leave a note about why this cast is appropriate, since otherwise at least to my eyes it seems out of place. Put a sign up on Chesterton's fence describing why it's there, in a sense :)
- Prefer lambda type annotations over inferred dict schema - For sequences that start with RunnableAssign infer seq input type as "input type of 2nd item in sequence - output type of runnable assign"
- Prefer lambda type annotations over inferred dict schema - For sequences that start with RunnableAssign infer seq input type as "input type of 2nd item in sequence - output type of runnable assign"
