AttributeError scikit learn pipeline based class

Question

I am trying to write a sklearn based feature extraction pipeline. My pipeline code idea could be splitted in few parts

1. A parent class where all data preprocessing (if required) could happen

from sklearn.base import BaseEstimator, TransformerMixin

class FeatureExtractor(BaseEstimator, TransformerMixin):
    """This is the parent class for all feature extractors."""
    def __init__(self, raw_data = {}):
        self.raw_data = raw_data

    def fit(self, X, y=None):
        return self

2. A decorator which helps one define the execution of feature extraction, for intelligently handling the case where one feature is dependent on another feature.

# A decorator to assign order of feature extraction within fearure extractor classes
def feature_order(order):
   def order_assignment(to_func):
       to_func.order = order
       return to_func
   return order_assignment

3. Finally one of the child class where all feature extraction is happening:

class ChilldFeatureExtractor1(FeatureExtractor):
   """This is the one of the child feature extractor class."""

   def __init__(self, raw_data = {}):
       super().__init__(raw_data)
       self.raw_data = raw_data

   @feature_order(1)
   def foo_plus_one(self):
       return self.raw_data['foo'] + 1

   # This feature extractor depends on value populated in previous feature extractor
   @feature_order(2)
   def foo_plus_one_plus_one(self):
       return self.raw_data['foo_plus_one'] + 1

   def transform(self):
       functions = sorted(
           #get a list of extractor functions with attribute order
           [
           getattr(self, field) for field in dir(self)
           if hasattr(getattr(self, field), "order")
           ],
           #sort the feature extractor functions by their order
           key = (lambda field: field.order)
           )

       for func in functions:
           feature_name = func.__name__
           feature_value = func()
           self.raw_data[feature_name] = feature_value

       return self.raw_data

Testing this code a small input:

if __name__ == '__main__':
    raw_data = {'foo': 1, 'bar': 2}
    fe = ChilldFeatureExtractor1(raw_data)
    print(fe.transform())

Gives error:

Traceback (most recent call last):
  File "/Users/temporaryadmin/deleteme.py", line 55, in <module>
    print(fe.transform())
  File "/Users/temporaryadmin/deleteme.py", line 37, in transform
    [
  File "/Users/temporaryadmin/deleteme.py", line 39, in <listcomp>
    if hasattr(getattr(self, field), "order")
  File "/Users/temporaryadmin/opt/miniconda3/envs/voutopia/lib/python3.8/site-packages/sklearn/base.py", line 450, in _repr_html_
    raise AttributeError("_repr_html_ is only defined when the "
AttributeError: _repr_html_ is only defined when the 'display' configuration option is set to 'diagram'

However when I don't inherit sklearn classes in base class ie. class FeatureExtractor(): then I get proper output:

{'foo': 1, 'bar': 2, 'foo_plus_one': 2, 'foo_plus_one_plus_one': 3}

Any pointer on this?

Answer 1

The error traceback indicates where this goes wrong: self has an attribute _repr_html_ listed in its __dir__, but trying to access it with getattr throws that ValueError, as shown in the source link from @maxskoryk's answer.

One fix is to give a default value in the getattr call:

   def transform(self):
       functions = sorted(
           #get a list of extractor functions with attribute order
           [
               getattr(self, field, None) for field in dir(self)
               if hasattr(getattr(self, field, None), "order")
           ],
           #sort the feature extractor functions by their order
           key = (lambda field: field.order),
       )
       ...

You could also just limit to attributes not starting with an underscore, or any other reasonable way to limit which attributes get checked.