Using an external function that takes in a float input as part of the problem objective

[TheRealWushuMaster]

Hi, everyone!

I'm creating an optimizer which will find the optimal combination of items to package together. Each item has its own weight.

The objective is to minimize the total cost of transporting said packages. The cost function (let's call it cost_function) depends on the total weight of the items in a package; it uses a float as the input (the weight of the package, in kg) and returns another float (the cost of transporting, in USD).

I have set up binary LpVariables that determine whether each item is included on each package, called x_i_j. These variables reflect whether the item i is included in the package j, and are equal to 1 if item i is in package j, or 0 otherwise.

The objective function needs to call cost_function to calculate the cost to use in the minimization problem. However, it's not possible to call cost_function right away, as the LpVariables are not float numbers, so I get an error similar to the following:

TypeError:` '<' not supported between instances of 'LpVariable' and 'float'

The previous error happens when the function tries to compare the weight input within a range.

Any ideas on how to fix this?
Thanks!