Why PyCups3 is So Damn Intelligent

In my last blog , I shared just how smart PyCups3 is. This time, let’s go one layer deeper and see why it’s so intelligent.

But first, let’s warm up with a bit of Python magic. ✨

What the Heck is a Dunder Method?

Straight from the Python 3.x docs:

Dunder methods (a.k.a. magic methods) are special methods you can define in your classes to give them superpowers. These methods let you make your class objects behave like built-in Python types. They’re called dunder because they start and end with a double underscore — like __init__.

Think of them as cheat codes for classes.

Enter PyCups3: Abstracting the Mess Away

PyCups3 is quietly doing a ton of heavy lifting for you.

Let me show you with one neat example: the enum IPPOp.

Life in C Land vs. Python Land

In libcups (C land), there’s no class structure, no properties, no pretty methods. You don’t expect to type IPPOp(2) and magically get back the corresponding enum.

But in Python land, things are more fun.

libcups3 has two handy APIs:

• ippOpString(enum_value) → gives you the string name of the enum
• ippOpValue(enum_string) → maps that string back to the enum value

So in C, you’d bounce between those two manually. But in Python, PyCups3 does some wizardry. 🪄

Trick #1: Making Enums String-Friendly

Normally, when you call str(object), Python looks for the object’s __str__ dunder method.

So I thought: why not hijack that for enums?

Here’s the magic sauce:

def __str__(self):
    return _bytes_to_value(_lib.ippOpString(self.value))

Now, when you do:

str(IPPOp.PRINT_JOB)

You don’t just get "IPPOp.PRINT_JOB" — you get the actual C API string. Pretty slick, right?

Trick #2: Turning Strings Back into Enums

Okay, but what if someone writes:

IPPOp("Print-Job")

and expects it to become IPPOp.PRINT_JOB?

That’s where another dunder steps in: _missing_.

@classmethod
def _missing_(cls, value):
    if isinstance(value, str):
        op = _lib.ippOpValue(value.encode())
        return cls(op)
    return None

This dunder gets triggered when the requested value doesn’t match anything in the enum. So if you pass a raw string, it politely asks ippOpValue to map it back. Boom — instant enum.

Why This Matters

These two examples are just the tip of the iceberg. PyCups3 is full of these subtle abstractions designed to make your life easier.

Because honestly — dealing with the CUPS architecture is already painful enough. Why make you wrestle with awkward APIs when Python can smooth it all out?

Wrapping Up

And that’s how PyCups3 quietly flexes its intelligence with a little help from Python dunders.

That’s all for today’s deep dive. I’ll be back with more fun PyCups3 tricks soon.

Until then, maybe I’ll see you at UbuCon Asia — or at least after it. 😉