How is "base" created?

I can’t seem to figure out how Panda’s initial python objects are loaded. Searching through all the files, I can’t find the line that defines base. ie., "base = … " How is it initialized?

It is in showbase.py, on line 305 of the init method for showebase.

__builtin__.base = self
        __builtin__.render2d = self.render2d
        __builtin__.aspect2d = self.aspect2d
        __builtin__.render = self.render
        __builtin__.hidden = self.hidden
        __builtin__.camera = self.camera
        __builtin__.loader = self.loader
        __builtin__.taskMgr = self.taskMgr
        __builtin__.jobMgr = self.jobMgr
        __builtin__.eventMgr = self.eventMgr
        __builtin__.messenger = self.messenger
        __builtin__.bboard = self.bboard
        # Config needs to be defined before ShowBase is constructed
        #__builtin__.config = self.config
        __builtin__.run = self.run
        __builtin__.ostream = Notify.out()
        __builtin__.directNotify = directNotify
        __builtin__.giveNotify = giveNotify
        __builtin__.globalClock = globalClock
        __builtin__.vfs = vfs
        __builtin__.cpMgr = ConfigPageManager.getGlobalPtr()
        __builtin__.cvMgr = ConfigVariableManager.getGlobalPtr()
        __builtin__.pandaSystem = PandaSystem.getGlobalPtr()
        __builtin__.wantUberdog = base.config.GetBool('want-uberdog', 1)
        if __debug__:
            __builtin__.deltaProfiler = DeltaProfiler.DeltaProfiler("ShowBase")
        __builtin__.onScreenDebug = OnScreenDebug.OnScreenDebug()

        if self.wantRender2dp:
            __builtin__.render2dp = self.render2dp
            __builtin__.aspect2dp = self.aspect2dp

Ah. ok. thanks. I don’t know Python very well, and didn’t know about
builtin

also see:
panda3d.org/manual/index.php/DirectStart