Question

I am developing in python a file class that can read and write a file, containing a list of xyz coordinates. In my program, I already have a Coord3D class to hold xyz coordinates.

My question is relative to the design of a getCoordinate(index) method. Should I return a tuple of floats, or a Coord3D object?

In the first case, I get very low coupling, but then I will probably have to instantiate a Coord3D object with the obtained values anyway, although outside of the file class. In the second case, I will have the file class tightly coupled with the Coord3D class.

Please note that I think there’s not a huge difference between the two solutions, but I would like to read your answer and the reason behind it.

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Edit: to recap the answers I got until now, it looks like there’s no clearcut choice. It has been said (appropriately) that python is not Java, and you don’t need a specialized class for everything just because you need it by language architecture. In my case, however, I have the following conditions:

1. I am working on a library, where the Coord3D object is used as is. Using it would increase the cohesiveness of my library, as the data types will be uniformly used.
2. The Coord3D object has state and behavior. Indeed, the Coord3D object aggregate the coordinates and the units in a single entity. Operations among Coord3D objects will keep into account the potentially different units, and act accordingly.
3. I can put centralize control code into the Coord3D class instantiation to refuse, for example, arrays of length 4, or non units. If I use a tuple, I cannot perform this check. Moreover, if a method accepts a Coord3D, is sort of guaranteed that it’s well formed upfront (you could be bold and check for isinstance, or check the interface). A tuple can contain invalid data. Although python approach to error handling is done where the trouble happen, a class preventing me to have an xyz coordinate made out of three strings is somehow beneficial (correct me if wrong, please)

On the other hand, using a tuple has the following advantages:

1. Less occupation of resources, quite critical in case of huge
2. Simpler design. More classes means more complex design. A tuple is a standard data type which is well understood and can be unpacked easily. A personalized class is not.
3. Using a tuple, the XYZFile class is totally decoupled from the rest of the library (because it does not use the Coord3D object). This means that it can be reused totally as an independent entity.

further comments very welcome!

Answer 1

I’ve asked myself the same question, albeit while doing 2D geometry stuff.

The answer I found for myself was that if I was planning to write a larger library, with more functions and whatnot, go ahead and return the Point, or in your case the Coord3D object. If it’s just a hacky implementation, the tuple will get you going faster. In the end, it’s just what you’re going to do with it, and is it worth the effort.