Generator for distributing calls

At work I was confronted with the problem of 'How to distribute calls between 2 call centers in a fair and even way according to some yet-to-be-determined percentage split ration?' Taking 30% split, we cannot send the first 30 to call centre 1 and the remaining 70 to call centre 2. The calls must be distributed as evenly as possible throughout; for example split 30% or 10 calls would give: [1,2,1,1,2,1,1,2,1,1] and not [1,1,1,1,1,1,1,2,2,2]!

When thinking about these kinds of problems, it helps to abstract away from the context of calls and call centres and think about the underlying problem; distribution over a descrete choice space. From here, we might find a solution in another domain that solves our problem...

It turns out that the problem of call distribution distils to the same problem that Bresenham tackled when trying to draw a line on a computer screen matrix. Imagine that you have a graph of cells 100 pixels on the X axis and 100 pixels on the Y axis. Now imagine you are using the line drawing algorithm to paint a line from the X/Y origin to, say, the coordinates '100,30'.

The line drawing algorithm will, after 100 interations, have distributed pixels evenly between 70 in the X direction and 30 in the Y direction (but always moving towards X). This is exactly the same as distributing 30 calls to call centre 1 and the rest to call centre 2.

To model this, it makes sense to write a python generator that 'yields' the correct call centre when asked:

class CallDistributor():
    def __init__(self, split=50):
        self.split = split
        if split > 100 or split <= 0:
            raise ValueError
 
    def _execute(self):
        error = 0.0
        step = 0
        deltaErr = self.split / 100.00
        yield 1
        while True:
            error += deltaErr
            if abs(error) >= 0.5:
                yield 2
                error -= 1.0
            else:
                yield 1
 
    def __iter__(self):
        return iter(self._execute( ))
 
 
if __name__ == "__main__":
    dist1 = CallDistributor(split=50)
    anIter = iter(dist1)
    for i in range(10):
        print anIter.next()

If I have chance I'd like to expand this to take a 'number of call centres' parameter, rather than having it restricted to 2.