PyO3 "`From<&PyCell<mod::struct>>` is not implemented for `f64`"

Question

I am trying to expose a Rust struct to Python class.

use pyo3::prelude::*;
use std::sync::Arc;
use indexmap::set::IndexSet;
use ndarray::{Array1, Array};

#[pyclass]
#[derive(Clone, Debug)]
pub struct Dual {
    real : f64,
    vars : Arc<IndexSet<String>>,
    dual : Array1<f64>,
}

#[pymethods]
impl Dual {
    fn new(real: f64, vars: Vec<String>, dual: Vec<f64>) -> Self {
        let new_dual;
        if dual.len() != 0 && vars.len() != dual.len() {
            panic!("`dual` must have same length as `vars` or have zero length.")
        } else if dual.len() == 0 && vars.len() > 0 {
            new_dual = Array::ones(vars.len());
        } else {
            new_dual = Array::from_vec(dual);
        }
        Self {
            real: real,
            vars: Arc::new(IndexSet::from_iter(vars)),
            dual: new_dual,
        }
    }

    fn __repr__(&self) -> String {
        return format!("<Dual: ... , [...], [...]>");
    }
}

When using maturin develop I get the error:

error[E0277]: the trait bound `f64: From<&PyCell<point::Dual>>` is not satisfied
  --> src\point\mod.rs:23:18
   |
23 |     fn new(real: f64, vars: Vec<String>, dual: Vec<f64>) -> Self {
   |                  ^^^ the trait `From<&PyCell<point::Dual>>` is not implemented for `f64`
   = help: the following other types implement trait `From<T>`:
             <f64 as From<bool>>
             <f64 as From<i8>>
             <f64 as From<i16>>
             <f64 as From<i32>>
             <f64 as From<u8>>
             <f64 as From<u16>>
             <f64 as From<u32>>
             <f64 as From<f32>>
   = note: required for `&PyCell<point::Dual>` to implement `Into<f64>`
   = note: required for `f64` to implement `TryFrom<&PyCell<point::Dual>>`

I do not understand this error, nor why, of all the types being used, this seems to fail on the basic float object.

If anyone can share any pointers or elucidate this error for me to help me learn what to do I would appreciate it.