import numpy as np
import matplotlib.pyplot as plt

nyc_temp_2000 = np.array([
    31.3, 37.3, 47.2, 51.0, 63.5, 71.3,
    72.3, 72.7, 66.0, 57.0, 45.3, 31.1
])
nyc_temp_2006 = np.array([
    40.9, 35.7, 43.1, 55.7, 63.1, 71.0,
    77.9, 75.8, 66.6, 56.2, 51.9, 43.6
])
nyc_temp_2012 = np.array([
    37.3, 40.9, 50.9, 54.8, 65.1, 71.0,
    78.8, 76.7, 68.8, 58.0, 43.9, 41.5
])

months = np.arange(1, 13)

fig, ax = plt.subplots()

ax.plot(months, nyc_temp_2000, marker="o", label="2000")
ax.plot(months, nyc_temp_2006, marker="o", label="2006")
ax.plot(months, nyc_temp_2012, marker="o", label="2012")

ax.set_title("Average monthly temperature in NYC")
ax.set_xlabel("Month")
ax.set_ylabel("Temperature")

ax.set_ylim(bottom=0)   # equivalent to axis(ymin=0)
ax.legend()

plt.show()