What variance threshold to consider in feature selection?
Usually 3 is taken as a threshold Value by standard deviation

Using z-score we can look for value above or below threshold like in code below: 

threshold=3
mean = np.mean(data)
std =np.std(data)

for x in data:
    z_score= (x - mean)/std 
    if np.abs(z_score) &gt; threshold:
        ...