def get_aperture_pos(sequence):
    """
    Calculate positions of apertures.

    Returns
    -------
    List of tuples with index and position of OPE in sequence.
    """
    d = 0.0
    d_ = []
    for idx, ope in enumerate(sequence):
        if ope.has_aperture():
            d_.append((idx, d))
        else:
            d += ope.get_travel_length()

    return d_