Getting TypeError: ‘(slice(None, None, None), 0)’ is an invalid key

Since you are trying to access directly as array, you are getting that issue. Try this:

from sklearn.impute import SimpleImputer
imputer = SimpleImputer(missing_values = np.nan, strategy = 'mean',verbose=0)
imputer = imputer.fit(X.iloc[:, 1:3])
X.iloc[:, 1:3] = imputer.transform(X.iloc[:, 1:3])

Using iloc/loc will resolve the issue.