plt.plot(count_by_year, '*-g')
plt.title('Books by year')
plt.xlabel('year')
plt.ylabel('number of books')
plt.xticks(range(1947, 2030, 10))
for idx, val in count_by_year[::5].items():
plt.annotate(val, (idx, val), xytext=(2, 2), textcoords='offset points')
plt.show()