data_handlers.py

# File: data_handlers.py
from models import MyDataObject

class MyDataHandler:
    """ responsible for working on the data only."""
    def __init__(self, data_object):
        self.data_object = data_object

    def mult_data_by_two(self):
        return self.data_object.numeric_data * 2

models.py

#File: models.py
class MyDataObject:
    """responsible for manipulating, transforming data"""

    def __init__(self):
        self.numeric_data = 0

    # this isn't really necessary in python, as one normally just sets/gets python attributes.
    # but, let's say that set does some crazy translation of the data, 
    # then it makes more sense to split into its own method
    def set_data(self, new_data):
        self.numeric_data = new_data

notebook.ipynb