<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _model_sanity(model):
 """ Perform some basic sanity checking on the model to warn users when they might be trying something ill advised. :param model: model instance. """

        if not isinstance(model, ODEModel) and not isinstance(model, BaseNumericalModel):
            # Such a model should probably not contain derivatives
            for var, expr in model.items():
                if isinstance(var, sympy.Derivative) or expr.has(sympy.Derivative):
                    warnings.warn(RuntimeWarning(
                        'The model contains derivatives in its definition. '
                        'Are you sure you don\'t mean to use `symfit.ODEModel`?'
                    ))