ValueError: pipeline named_steps KeyError

ValueError: named_steps KeyError

$ python -c "from sklearn.pipeline import Pipeline; p=Pipeline([('scale', None)]); p.named_steps['scaler']"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
KeyError: 'scaler'

Why this happens

Accessing a non-existent key in named_steps raises KeyError. Typos or different step names are common causes.

Fix

Use the exact step name or iterate named_steps.keys() to confirm available names.

Wrong code

from sklearn.pipeline import Pipeline
pipe = Pipeline([('scaler', None), ('clf', None)])
pipe.named_steps['scale']  # typo

Fixed code

from sklearn.pipeline import Pipeline
pipe = Pipeline([('scaler', None), ('clf', None)])
pipe.named_steps['scaler']  # correct key