fix(rust, python): allow extract of numeric from str AnyValue

[mcrumiller]

Resolves #13862.

Not completely sure this is the way to go, but the reason the error is occuring is because the frame creation using a series of dicts involves adding records row-by-row to the frame. The result is the use of the AnyValueBuffer::add_fallible() which in turn calls AnyValue::extract() on the read value. If the read value is str and the target is int, AnyValue::extract would panic. This adds a branch which tries to cast the string to an int, so the conversion will succeed for valid ints.

[ritchie46]

I don't think we should do this this way. See my comment in issue. In any case the i64 is completely arbitrary. It could also be a float.

[mcrumiller]

Ok I totally agree that the implementation is bad, unsure how to align with Series/Expr though.

As an aside, I am trying to figure out why pl.lit("1").cast(pl.UInt8) succeeds when the AnyValue::cast function returns an Error. It looks like the optimizer is somehow taking a different path which doesn't error:

pl.select(pl.lit("1").cast(pl.UInt8))  # succeeds

[ritchie46]

Yes, it goes though the Series cast function. The AnyValue is only meant a simple optimization. When stuff gets more opinionated or complex it should go through the dedicated function for columns.

[mcrumiller]

Ok. Should I close this, or do we still want to address the associated issue?

[ritchie46]

I think this one can be closed. It would be worth it if we got a better error message for this one.

[ritchie46]

Hmm.. Sorry for the confusion @mcrumiller. I thought we were somewhere else in the codebase.

This might work if we get more information on how to parse the string. E.g. do we need to parse as either f64 or i128 (we also must fit u64).