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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 import_obj(file_name, **kwargs):
 """ Reads .obj files and generates faces. Keyword Arguments: * ``callback``: reference to the function that processes the faces for customized output The structure of the callback function is shown below: .. code-block:: python def my_callback_function(face_list):
 # "face_list" will be a list of elements.Face class instances # The function should return a list return list() :param file_name: file name :type file_name: str :return: output of the callback function (default is a list of faces) :rtype: list """

    def default_callback(face_list):
        return face_list

    # Keyword arguments
    callback_func = kwargs.get('callback', default_callback)

    # Read and process the input file
    content = exch.read_file(file_name)
    content_arr = content.split("\n")

    # Initialize variables
    on_face = False
    vertices = []
    triangles = []
    faces = []

    # Index values
    vert_idx = 1
    tri_idx = 1
    face_idx = 1

    # Loop through the data
    for carr in content_arr:
        carr = carr.strip()
        data = carr.split(" ")
        data = [d.strip() for d in data]
        if data[0] == "v":
            if on_face:
                on_face = not on_face
                face = elements.Face(*triangles, id=face_idx)
                faces.append(face)
                face_idx += 1
                vertices[:] = []
                triangles[:] = []
                vert_idx = 1
                tri_idx = 1
            vertex = elements.Vertex(*data[1:], id=vert_idx)
            vertices.append(vertex)
            vert_idx += 1
        if data[0] == "f":
            on_face = True
            triangle = elements.Triangle(*[vertices[int(fidx) - 1] for fidx in data[1:]], id=tri_idx)
            triangles.append(triangle)
            tri_idx += 1

    # Process he final face
    if triangles:
        face = elements.Face(*triangles, id=face_idx)
        faces.append(face)

    # Return the output of the callback function
    return callback_func(faces)