Example of classmethod for class polymorphism and different constructors

classmethod.py

# Python only supports a single constructor per class, the __init__ method. 
# Use @classmethod to define alternative constructors for your classes.
# Use class method polymorphism to provide generic ways to build and connect concrete subclasses.


class GenericInputData(object):
    
    def read(self):
        raise NotImplementedError
        
    @classmethod
    def generate_inputs(cls, config):
        raise NotImplementedError

class PathInputData(GenericInputData): 
    
    def __init__(self, file_path):
        self.file_path = file_path
    
    def read(self):
        return open(self.path).read()
    
    @classmethod
    def generate_inputs(cls, config):
        """Generators that create a PathInputData Object
        for each file in config[‘data_dir’]
        """
        data_dir = config[‘data_dir’]
        for name in os.listdir(data_dir):
            yield cls(os.path.join(data_dir, name)) # Generate a new object for each file in data_dir