Best object oriented Python construct to use for particular application

Question

I have a class with one method which outputs a dict. The class needs a file_path to be instantiated. The method needs a string parameter to output the dict. Here is some pseudo-code.

class A():
    def __init__(self, file_path):
        self.file_path = file_path
    def create_dict(self, param):
        #uses self.filepath
        #creates a dict called data. The dict contains 2 keys and each key contains a list. The first list is a list of strings and the second a list of integers
        return data

The procedure to generate this dict is irrelevant in my opinion. The final output is as follows:

data = {'Key1': ['String1', 'String2', 'String3',....], 'Key2': [1,2,4,....]}

When I started to implement this class I noticed that I wanted to have data be an object instead. This object would have methods data.printKey1() and data.printKey2() which would output the following:

>>> data.printKey1()
String1
String2
String3 
...
>>>data.printKey2()
1
2
4

Now I'm stuck because I really don't want to reconstruct the whole procedure by which data is generated, but I need it to be an object.

I am not sure whether I should use inheritance, class containment or composition (or some other construct I am unaware of). In theory, what is the best practice to use here? How can I generate this new data class/object without having to rework the entire procedure contained in the create_dict method?

Answer 1

Do you really need a class for this ? a simple function would work:

def printkey(data, key):
    for line in data[key]:
        print(line)

printkey(data, "key1")
printkey(data, "key2")

Actually, mixing domain logic with presentation is a well known antipattern. If you really want a class (to make some narrow-minded OO purist happy or for better reasons that are not explained in your question), then you can of course write some "presenter" class:

class DataPrinter(object):
    def __init__(self, data):
        self.data = data

    def _printkey(self, key):
        for line in self.data[key]:
            print(line)

    def printkey1(self):
        self._printkey("key1")

    def printkey2(self):
        self._printkey("key2")

but that's really mostly useless IMHO, at least for the given example (it might make sense for some much more complex data model and presentation stuff).

Oh and yes, FWIW, Python functions ARE objects (instances of class function) so you can just tell some-narrow-minded-OO-purist that the function-based solution IS actually proper OO design too xD (poor Java dudes had to invent a design pattern - the "functor" - to hide the fact that sometimes all you need is a plain old function...).