mask = np.triu(np.ones_like(df.corr(), dtype=bool))
cmap = sns.diverging_palette(230, 20, as_cmap=True)
f, ax = plt.subplots(figsize=(20,20))
sns.heatmap(df.corr(), mask=mask, vmax=.3, center=0,
square=True, linewidths=.5, cbar_kws={"shrink": .5},annot=True,fmt='.2f')
