Generate the string from `__str__` method.

        Parameters
        ----------
        phi_or_p: 'phi' | 'p'
                'phi': When used for Factors.
                  'p': When used for CPDs.
        print_state_names: boolean
                If True, the user defined state names are displayed.

def _str(self, phi_or_p="phi", tablefmt="grid", print_state_names=True):
        """
        Generate the string from `__str__` method.

        Parameters
        ----------
        phi_or_p: 'phi' | 'p'
                'phi': When used for Factors.
                  'p': When used for CPDs.
        print_state_names: boolean
                If True, the user defined state names are displayed.
        """
        string_header = list(map(lambda x: six.text_type(x), self.scope()))
        string_header.append('{phi_or_p}({variables})'.format(phi_or_p=phi_or_p,
                                                              variables=','.join(string_header)))

        value_index = 0
        factor_table = []
        for prob in product(*[range(card) for card in self.cardinality]):
            if self.state_names and print_state_names:
                prob_list = ["{var}({state})".format(
                    var=list(self.variables)[i], state=self.state_names[list(
                        self.variables)[i]][prob[i]])
                             for i in range(len(self.variables))]
            else:
                prob_list = ["{s}_{d}".format(s=list(self.variables)[i], d=prob[i])
                             for i in range(len(self.variables))]

            prob_list.append(self.values.ravel()[value_index])
            factor_table.append(prob_list)
            value_index += 1

        return tabulate(factor_table, headers=string_header, tablefmt=tablefmt, floatfmt=".4f")