def get_walkID(filename):
    """Create walkID from filename.

    Args:
        filename (str): contains 3 substrings
            'trial_[trial_num]'
            'walklr_[walk_side]'
            'visit_[visit_num']

    Returns:
        walkID (str): formatted as [trial_num]-[walk_side]-[visit_num]
    """
    trial = filename.split('trial_')[-1].split('.')[0]
    walk = filename.split('walklr_')[-1].split('_')[0]
    visit = filename.split('visit_')[-1].split('_')[0]
    walkID = trial + '-' + walk + '-' + visit
    return walkID