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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sum(self, phi1, inplace=True):
 """ DiscreteFactor sum with `phi1`. Parameters phi1: `DiscreteFactor` instance. DiscreteFactor to be added. inplace: boolean If inplace=True it will modify the factor itself, else would return a new factor. Returns ------- DiscreteFactor or None: if inplace=True (default) returns None if inplace=False returns a new `DiscreteFactor` instance. Example ------- ['x1', 'x2', 'x3', 'x4'] array([2, 3, 2, 2]) array([[[[ 0, 0], [ 4, 6]], [[ 0, 4], [12, 18]], [[ 0, 8], [20, 30]]], [[[ 6, 18], [35, 49]], [[ 8, 24], [45, 63]], [[10, 30], [55, 77]]]]) """

        phi = self if inplace else self.copy()
        if isinstance(phi1, (int, float)):
            phi.values += phi1
        else:
            phi1 = phi1.copy()

            # modifying phi to add new variables
            extra_vars = set(phi1.variables) - set(phi.variables)
            if extra_vars:
                slice_ = [slice(None)] * len(phi.variables)
                slice_.extend([np.newaxis] * len(extra_vars))
                phi.values = phi.values[tuple(slice_)]

                phi.variables.extend(extra_vars)

                new_var_card = phi1.get_cardinality(extra_vars)
                phi.cardinality = np.append(phi.cardinality, [new_var_card[var] for var in extra_vars])

            # modifying phi1 to add new variables
            extra_vars = set(phi.variables) - set(phi1.variables)
            if extra_vars:
                slice_ = [slice(None)] * len(phi1.variables)
                slice_.extend([np.newaxis] * len(extra_vars))
                phi1.values = phi1.values[tuple(slice_)]

                phi1.variables.extend(extra_vars)
                # No need to modify cardinality as we don't need it.

            # rearranging the axes of phi1 to match phi
            for axis in range(phi.values.ndim):
                exchange_index = phi1.variables.index(phi.variables[axis])
                phi1.variables[axis], phi1.variables[exchange_index] = phi1.variables[exchange_index], \
                    phi1.variables[axis]
                phi1.values = phi1.values.swapaxes(axis, exchange_index)

            phi.values = phi.values + phi1.values

        if not inplace:
            return phi