[FIXED] How do I know whether a sklearn scaler is already fitted or not?

Issue

For example, ss is an sklearn.preprocessing.StandardScaler object. If ss is fitted already, I want to use it to transform my data. If ss is not fitted yet, I want to use my data to fit it and transform my data. Is there a way to know whether ss is already fitted or not?

Solution

Sklearn implements the check_is_fitted function to check if any generic estimator is fitted, which works with StandardScaler:

from sklearn.preprocessing import StandardScaler
from sklearn.utils.validation import check_is_fitted

ss = StandardScaler()
check_is_fitted(ss) # Raises error

ss.fit([[1,2,3]])
check_is_fitted(ss) # No error

Answered By - EEtch