@property<EOL><INDENT>def solver(self):<DEDENT>
return self._solver<EOL>
Get or set the attached solver instance.

        The associated the solver object, which manages the interaction with
        the associated solver, e.g. glpk.

        This property is useful for accessing the optimization problem
        directly and to define additional non-metabolic constraints.

        Examples
        --------
        >>> import cobra.test
        >>> model = cobra.test.create_test_model("textbook")
        >>> new = model.problem.Constraint(model.objective.expression,
        >>> lb=0.99)
        >>> model.solver.add(new)