This is my part of code, why it shows: TypeError: unsupported operand type(s) for /: 'list' and 'list'
<Figure size 576x288 with 0 Axes>
plt.figure(figsize=(8, 4))
plt.scatter(p_vol, p_ret,c=p_ret / p_vol, marker='o')
plt.scatter(t_vol, trets,c=trets / t_vol, marker='x')
plt.plot(statistics(opts['x'])[1], statistics(opts['x'])[0],'r*', markersize=15.0)
# portfolio with highest Sharpe ratio
plt.plot(statistics(optv['x'])[1], statistics(optv['x'])[0],'y*', markersize=15.0)
# minimum variance portfolio
plt.grid(True)
plt.xlabel('expected volatility')
plt.ylabel('expected return')
plt.colorbar(label='Sharpe ratio')