🔒 Affirm to checker that method will return value in use case

[hard dust]

I'm positive this has been answered, but I'm not able to find the response, probably because I'm not searching the right terms.

I have this code:

object_session(self).scalars(

object_session(self) can returns Session | None, but in this use case, I know it will return a Session. How can I make the checker (ruff) happy with the line? I know I could do something like

session = object_session(self)
if not session:
  raise Exception()
session.scalars

But that's wordy, specially as if there's no session, there would have been a problem upstream anyway.

[analog crest]

Hey @hard dust!

Please edit your message to use a code block

Add a py after the three backticks.

```py
print('Hello, world!')
```

This will result in the following:

print('Hello, world!')```

[analog crest]

@hard dust

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[silk nacelle]

You can either do an assertion: assert isinstance(session, Session)
Or you can use typing.cast (the function below, typing.assert_type, also seems useful):
https://docs.python.org/3/library/typing.html#typing.cast

[hard dust]

Ok, so safety checks, same as my idea of checking if None

Which is the "right" way to do it anyway

[mossy ermine]

the right thing to do would be try to go upstream and figure out how to encode this information within the types itself. That is, your method should only return a Session in this case. besides that, you have many options:

• assert session
• session = typing.cast(Session, object_session(self))
• # type: ignore
  and probably more

[hard dust]

Well, in this case, object_session is coming from SqlAlchemy, so I can't force that

I know it will return a session, as the method I'm writing requires there to be a value from the database, so a session would have to be attached anyway

And if something goes wrong with the session, I'd want an exception

[copper lake]

"as the method I'm writing requires there to be a value from the database" - suppose it's missing anyway; what would have happened before the code gets to this point?

[analog crest]

Python help channel closed for inactivity

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