A small python question....

Scripting Issues
1

…regarding scope.

I noticed a bit of variance between tutorials/code snippets etc.

If I have a class inheriting from ShowBase, I can make a calls such as:

myObject.reparentTo(render)

Or:

myObject.reparentTo(self.render)

I can also make calls to base:

base.camera.setPos(...)

Though self does not apply:

self.base.... [ error ]

Although base seems to be the same as self:

self.camera.setPos(...)  [ works ]

So what’s the deal with Python and the self keyword here? To my understanding, a member variable would be declared via self.someVar …and later referenced via self.someVar too. Absence of self implies a local variable that drops out of scope post-method.

Why do I not need the self keyword for render?
Why do I not need the self keyword for base?

Could be me being a thick Python n00b, but thought I’d ask!

Cheers,
~G

2

Instaniating showbase also generates a bunch of global variables that point to things inside your showbase class.

Things like render and camera

In other words

render=base.render
camera = base.camera
… etc.

Take a look at the Showbase.py in the direct/showbase directory

3

Thanks!

Though what’s the benefit of having these as globals? Kinda breaks all the rules in this Old Skool head of mine!

Cheers,
~G

4

It certainly does break rules. This kind of builtin stuffing was done back when Panda was just an internal tool for a small group of people. It doesn’t make as much sense for a robust middleware graphics engine to do this, but now we’re stuck with it because too much existing code relies on it.

Panda3D 2.0 won’t do this kind of thing.

David

5

I was curious about this as well.

I notice a lot of example inherit directObject rather than showbase. Is the prefered method going forward not to use showbase at all?

6

That’s a stylistic thing. I don’t think it matters much whether you inherit from ShowBase or not; but you need to instantiate a ShowBase in order to open a window (unless you want to write all of the ShowBase code yourself); and you also need a place to put your own application-specific code, so it often makes sense to put it in class that inherits from ShowBase. But there’s no requirement that you do so.

David