CODEWITHSUNDEEP
pythonclassobjectpython-2.7instance
Dan Oberlam
Dan Oberlam

Reputation: 2496

Is it possible to create unique instances that have the same input?

I am working on code in Python that creates Compound objects (as in chemical compounds) that are be composed of Bond and Element objects. These Element objects are created with some inputs about them (Name, symbol, atomic number, atomic mass, etc). If I want to populate an array with Element objects, and I want the Element objects to be unique so I can do something to one and leave the rest unchanged, but they should all have the information related to a 'Hydrogen' element.

This question Python creating multiple instances for a single object/class leads me to believe that I should create sub-classes to Element - ie a Hydrogen object and a Carbon object, etc.

Is this doable without creating sub-classes, and if so how?

Upvotes: 1

Views: 253

Answers (1)

abarnert
abarnert

Reputation: 365905

Design your object model based on making the concepts make sense, not based on what seems easiest to implement.

If, in your application, hydrogen atoms are a different type of thing than oxygen atoms, then you want to have a Hydrogen class and an Oxygen class, both probably subclasses of an Element class.*

If, on the other hand, there's nothing special about hydrogen or oxygen (e.g., if you don't want to distinguish between, say, oxygen and sulfur, since they both have the same valence), then you don't want subclasses.

Either way, you can create multiple instances. It's just a matter of whether you do it like this:

atoms = [Hydrogen(), Hydrogen(), Oxygen(), Oxygen()]

… or this:

atoms = [Element(1), Element(1), Element(-2), Element(-2)]

If your instances take a lot of arguments, and you want a lot of instances with the same arguments, repeating yourself like this can be a bad thing. But you can use a loop—either an explicit statement, or comprehension—to make it better:

for _ in range(50):
    atoms.append(Element(group=16, valence=2, number=16, weight=32.066))

… or:

atoms.extend(Element(group=16, valence=2, number=16, weight=32.066) 
             for _ in range(50))

* Of course you may even want further subclasses, e.g., to distinguish Oxygen-16, Oxygen-17, Oxygen-18, or maybe even different mixtures, like the 99.762% Oxygen-16 with small amounts of -18 and tiny bits of the others that's standard in Earth's atmosphere, vs. the different mixture that was common millions of years ago…

Upvotes: 6

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