def vertex_indices_in_segments(self, segments, ret_face_indices=False):
        '''
        Given a list of segment names, return an array of vertex indices for
        all the vertices in those faces.

        Args:
            segments: a list of segment names,
            ret_face_indices: if it is `True`, returns face indices
        '''
        import numpy as np
        import warnings

        face_indices = np.array([])
        vertex_indices = np.array([])
        if self.segm is not None:
            try:
                segments = [self.segm[name] for name in segments]
            except KeyError as e:
                raise ValueError('Unknown segments {}. Consier using Mesh.clean_segments on segments'.format(e.args[0]))
            face_indices = np.unique(np.concatenate(segments))
            vertex_indices = np.unique(np.ravel(self.f[face_indices]))
        else:
            warnings.warn('self.segm is None, will return empty array')

        if ret_face_indices:
            return vertex_indices, face_indices
        else:
            return vertex_indices
Given a list of segment names, return an array of vertex indices for
        all the vertices in those faces.

        Args:
            segments: a list of segment names,
            ret_face_indices: if it is `True`, returns face indices