def compute_time_serie(time_serie, operation):
    """Given a time series in the form
        
        [(x, 10), (y, 20), (z, 15)]
    
    and an operation of the form
        lambda v1: v1 * 2
    return
        [(x, 20), (y, 40), (z, 30)]
    """
    return [tuple((pair[0], operation(pair[1]))) for pair in time_serie]