Question

I’m looking for a generic algorithm which, given the range values start and end will generate a list of numbers, but the numbers must go through zero..
Here’s my current code:

end = 78
start = -1 * end
step_size = 16
numbers = range(start, end+step_size, step_size)

$ numbers
Out[90]: [-78, -62, -46, -30, -14, 2, 18, 34, 50, 66, 82]

so in this particular case, I would subtract 2 from each number, so that the numbers have one zero value. But how could I do this more generally? I’m doing this to calculate the y-tic locations of a graph, and therefore I want them to go through zero once.

Answer 1

start % step_size should be the required offset:

>>> end = 78
>>> start = -1 * end
>>> step_size = 16
>>> range(start-(start%step_size), end+step_size, step_size)
[-80, -64, -48, -32, -16, 0, 16, 32, 48, 64, 80]

Examples:

def get_range(end, step_size):
    start = -1 * end
    return range(start-(start%step_size), end+step_size, step_size)

>>> get_range(23, 4)
[-24, -20, -16, -12, -8, -4, 0, 4, 8, 12, 16, 20, 24]
>>> get_range(19, 11)
[-22, -11, 0, 11, 22]
>>> get_range(103, 32)
[-128, -96, -64, -32, 0, 32, 64, 96, 128]