Function to_isize_index

crates/vm/src/sliceable.rs:454–468

Go from PyObjectRef to isize w/o overflow error, out of range values are substituted by isize::MIN or isize::MAX depending on type and value of step. Equivalent to PyEval_SliceIndex.

(vm: &VirtualMachine, obj: &PyObject)

// isize::MIN or isize::MAX depending on type and value of step.
// Equivalent to PyEval_SliceIndex.
fn to_isize_index(vm: &VirtualMachine, obj: &PyObject) -> PyResult<Option<isize>> {
    if vm.is_none(obj) {
        return Ok(None);
    }
    let result = obj.try_index_opt(vm).unwrap_or_else(|| {
        Err(vm.new_type_error("slice indices must be integers or None or have an __index__ method"))
    })?;
    let value = result.as_bigint();
    let is_negative = value.is_negative();
    Ok(Some(value.to_isize().unwrap_or(if is_negative {
        isize::MIN
    } else {
        isize::MAX
    })))
}