def get_no_aliens(sett, alien_width):
    """Determine the number of aliens that fit in a row.
     Spacing between each alien is equal to half alien width"""

    available_space_x = sett.screen_width - 1.5 * alien_width
    no_of_aliens = int(available_space_x / (1.5 * alien_width))
    return no_of_aliens