Below is an example of how to use the symfit.core.models.CallableNumericalModel. This class allows you to provide custom callables as your model, while still allowing clean interfacing with the symfit API.
These models also accept a mixture of symbolic and callable components, as will be demonstrated below. This allows the power-user great flexibility, since it is still easy to interface with symfit's constraints, minimizers, etc.
../../examples/callable_numerical_model.py
This is the resulting fit:
