Bandwidth.

    Formula:
    BW = SMA(H - L)

def band_width(high_data, low_data, period):
    """
    Bandwidth.

    Formula:
    BW = SMA(H - L)
    """
    catch_errors.check_for_input_len_diff(high_data, low_data)
    diff = np.array(high_data) - np.array(low_data)
    bw = sma(diff, period)
    return bw