fig_1 = plt.figure(1, figsize=(6.4, 4.8))
chart_1 = fig_1.add_subplot(121)
chart_2 = fig_1.add_subplot(122)
chart_1.plot(year, apl_price)
chart_2.plot(year, ms_price)
plt.show()

fig_1 = plt.figure(1, figsize=(6.4, 4.8))
chart_1 = fig_1.add_subplot(121)
chart_2 = fig_1.add_subplot(122)
chart_1.plot(year, apl_price)
chart_2.plot(year, ms_price)
plt.show()

I suppose you're using matplolib, you can use matplotlib.pyplot.xlabel and matplotlib.pyplot.ylabel :
matplotlib.pyplot.xlabel
matplotlib.pyplot.ylabel