From the example set by @lilpuggy in a previous exercise, you can also use numpy arrays instead of list comprehension to solve this:
import numpy as np
#your work here
ax = plt.subplot(1, 1, 1)
plt.plot(range(len(revenue)), revenue)
ax.set_xticks(months)
ax.set_xticklabels(month_names, rotation=30)
y_upper = np.array(revenue) + np.array(revenue)*0.1
y_lower = np.array(revenue) - np.array(revenue)*0.1
plt.fill_between(months, y_lower, y_upper, alpha=0.2)
plt.show()
Cheers! 