samedi 12 septembre 2020

Pythonic way of reducing the subclasses

background: so, I am working on an NLP problem. where I need to extract different types of features based on different types of text documents. and I currently have a setup where there is a FeatureExtractor base class, which is subclassed multiple times depending on the different types of docs and all of them calculate a different set of features and return a pandas data frame as output.

all these subclasses are further called by one wrapper type class called FeatureExtractionRunner which calls all the subclasses and calculates the features on all docs and returns the output for all types of docs.

Problem: this pattern of calculating features leads to lots of subclasses. currently, I have like 14 subclasses, since I have 14 types of docs.it might expand further. and this is too many classes to maintain. Is there an alternative way of doing this? with less subclassing

here is some sample representative code of what i explained:

from abc import ABCMeta, abstractmethod

class FeatureExtractor(metaclass=ABCMeta):
    #base feature extractor class
    def __init__(self, document):
        self.document = document
        
        
    @abstractmethod
    def doc_to_features(self):
        return NotImplemented
    
    
class ExtractorTypeA(FeatureExtractor):
    #do some feature calculations.....
    
    def _calculate_shape_features(self):
        return None
    
    def _calculate_size_features(self):
        return None
    
    def doc_to_features(self):
        #calls all the fancy feature calculation methods like 
        f1 = self._calculate_shape_features(self.document)
        f2 = self._calculate_size_features(self.document)
        #do some calculations on the document and return a pandas dataframe by merging them  (merge f1, f2....etc)
        data = "dataframe-1"
        return data
    
    
class ExtractorTypeB(FeatureExtractor):
    #do some feature calculations.....
    
    def _calculate_some_fancy_features(self):
        return None
    
    def _calculate_some_more_fancy_features(self):
        return None
    
    def doc_to_features(self):
        #calls all the fancy feature calculation methods
        f1 = self._calculate_some_fancy_features(self.document)
        f2 = self._calculate_some_more_fancy_features(self.document)
        #do some calculations on the document and return a pandas dataframe (merge f1, f2 etc)
        data = "dataframe-2"
        return data
    
class ExtractorTypeC(FeatureExtractor):
    #do some feature calculations.....
    
    def doc_to_features(self):
        #do some calculations on the document and return a pandas dataframe
        data = "dataframe-3"
        return data

class FeatureExtractionRunner:
    #a class to call all types of feature extractors 
    def __init__(self, document, *args, **kwargs):
        self.document = document
        self.type_a = ExtractorTypeA(self.document)
        self.type_b = ExtractorTypeB(self.document)
        self.type_c = ExtractorTypeC(self.document)
        #more of these extractors would be there
        
    def call_all_type_of_extractors(self):
        type_a_features = self.type_a.doc_to_features()
        type_b_features = self.type_b.doc_to_features()
        type_c_features = self.type_c.doc_to_features()
        #more such extractors would be there....
        
        return [type_a_features, type_b_features, type_c_features]
        
        
all_type_of_features = FeatureExtractionRunner("some document").call_all_type_of_extractors()

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