Using input variable for setting up material characteristics

[Patapain33]

Hi everyone,
I have an issue with a project of mine in which I need to make a parametric study on Fluent, using different values of specific heat for my fluid and solid materials :

For that reason, I want to make it so that instead of using the option "constant" for the specific heat, I can use my input parameter "fluid_cp" as shown below :

I can do it just fine from the Fluent window, but when I try to do it from pyfluent, I get this error :

It seems that my input parameter isn't something that I can select as my "option" for the material.
Does anyone have any idea of how I could bypass that issue ?

Thanks very much in advance

PS : the line I used in pyfluent is this one :