Pipelines de transformation chapitre 2

Bonjour,
J'ai eu ce problème:

```python
#Pipeline de transformation des colonnes numériques
from sklearn.pipeline import Pipeline
from sklearn.preprocessing import StandardScaler
num_pipeline = Pipeline([("imputer", SimpleImputer(strategy="median")), ("attribs_adder", CombinedAttributesAdder()), ("std_scaler", StandardScaler())])
housing_num_tr = num_pipeline.fit_transform(housing_num)
```

Et ceci comme erreur:

```
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
in
2 from sklearn.pipeline import Pipeline
3 from sklearn.preprocessing import StandardScaler
----> 4 num_pipeline = Pipeline([("imputer", SimpleImputer(strategy="median")), ("attribs_adder", CombinedAttributesAdder()), ("std_scaler", StandardScaler())])
5 housing_num_tr = num_pipeline.fit_transform(housing_num)

NameError: name 'CombinedAttributesAdder' is not defined
```

Puis-je avoir de l'aide?
Merci