def bandwidth(data, period, std=<NUM_LIT>):
catch_errors.check_for_period_error(data, period)<EOL>period = int(period)<EOL>bandwidth = ((upper_bollinger_band(data, period, std) -<EOL>lower_bollinger_band(data, period, std)) /<EOL>middle_bollinger_band(data, period, std)<EOL>)<EOL>return bandwidth<EOL>
Bandwidth.

Formula:
bw = u_bb - l_bb / m_bb