Lines over Heatmap

lined_heatmap.py

import seaborn as sns; sns.set()
import matplotlib.pyplot as plt
flights = sns.load_dataset("flights");flights = flights.pivot("month", "year", "passengers")
fig, ax = plt.subplots(1, figsize=(16,8))         
sns.heatmap(flights, cbar=False, annot=True, fmt='.0f', ax=ax)
for ix in range(12):   # one per height
    x = range(12); y = ix+1-flights.iloc[ix]/flights.iloc[ix].max()
    h = plt.plot(x,y, lw=4)
plt.show()