cannot import name 'imputer' from 'sklearn' code example

Example 1: cannot import name 'imputer'

from sklearn.impute import SimpleImputer 
imputer = SimpleImputer(missing_values=np.nan, strategy='mean')

Example 2: cannot import name 'imputer' from 'sklearn.preprocessing'

from sklearn.impute import SimpleImputer
imputer = SimpleImputer(missing_values=np.nan, strategy='mean')