global/local variables

[Tim Rau]

What makes python decide whether a particular variable is global or
local? I've got a list and a integer, both defined at top level, no
indentation, right next to each other:

allThings = []
nextID = 0

and yet, in the middle of a function, python sees one and doesn't see
the other:

class ship(thing):
###snip###
    def step(self):
###snip###
        if keys[K_up]
            for n in range(0,2):  #sparks/newton second is
proportional to framerate
                divergence = 5.0
                p = self.body.getRelPointPos((-0.15,0,0))
                v = self.body.vectorToWorld((-100+ random.uniform(-
divergence,divergence) ,random.uniform(-divergence,divergence),0))
                allThings.append(particle(p,v))
                allThings[len(allThings)-1].id = nextID
                nextID += 1


I don't think it's important, but the function is defined before the
two globals. What gives?