As I mentioned here it might make sense to deprecate setting pipeline steps to None and requiring "passthrough" instead to avoid ambiguities with FeatureUnion and ColumnTransformer.
This might also give us an opportunity to easily specify "blank" pipelines for which you want to search the steps. Right now it's not easy to say "I want a pipeline with three steps and then let the GridSearch figure out the steps" because you need to provide actual steps at instantiation.
Something like
pipe = Pipeline([("imputer", "passthrough"), ("scaler", "passthrough"), ("classifier", "passthrough")])or something.
As I mentioned here it might make sense to deprecate setting pipeline steps to
Noneand requiring"passthrough"instead to avoid ambiguities with FeatureUnion and ColumnTransformer.This might also give us an opportunity to easily specify "blank" pipelines for which you want to search the steps. Right now it's not easy to say "I want a pipeline with three steps and then let the GridSearch figure out the steps" because you need to provide actual steps at instantiation.
Something like
or something.