Function pyo3_macros_backend::params::impl_arg_param

fn impl_arg_param(
    arg: &FnArg<'_>, 
    spec: &FnSpec<'_>, 
    idx: usize, 
    self_: Option<&Type>, 
    option_pos: &mut usize, 
    py: &Ident, 
    args_array: &Ident
) -> Result<TokenStream>

Re option_pos: The option slice doesn’t contain the py: Python argument, so the argument index and the index in option diverge when using py: Python