import re


def list_faces_ids(faces):
    """
    This function analyse the faces name and extract the id.
    e.i. for and element as "polyMesh.f[35]", it extract 35.
    This return a list of int.
    """
    ids = []
    for face in faces:
        facename = re.findall(".f\[\d*\]", face)[0]
        id_ = int([elt for elt in re.findall(r"\d*", facename) if elt][0])
        ids.append(int(id_))
    return ids