Generates the coordinates for a spiral!

spiral.py

"""
Displays the coordinates used to draw a circle.

Assumes top of the circle is (0,0)
- positive X = right
- positive y = down

To run on a spiral of width 3:
spiral.py -s 3
"""
from optparse import OptionParser
__version_info__ = ('1', '2', '3')
__version__ = '.'.join(__version_info__)

def spiral(width):
    """
    Generate a spiral in a recursive fashion.  Assumes that the top of the screen is (0,0)
    """
    
    if( width < 1 ):
        return None
    elif( width == 1 ):
        return (0,0)
    else:
        return spiral_r(width, 0)
    

def spiral_r(width, depth):
    if( width == 2 ):
        return [(depth, depth),(depth+1,depth),(depth+1,depth+1),(depth,depth+1)]
    elif( width == 1 ):
        # base case
        return [(depth, depth)]
    else:
        # recursive case
        buffer = []
        for i in range(width):
            # right width
            buffer += [(i, depth) for i in range(depth, depth + width)]
                
            # down width -1
            buffer += [(depth + width - 1, depth + i) for i in range(depth + 1, depth + width)]
            
            # left width -1
            buffer += [(i, depth + width - 1) for i in range(depth+width-2,depth-1,-1)]
            
            # up width - 2
            buffer += [(depth,i) for i in range(depth+width-2,depth,-1)]
            
            # append recursive answer
            return buffer + spiral_r(width - 2, depth + 1)
            
if __name__ == '__main__':
    # print out a test case
    parser = OptionParser(version=__version__)
    parser.add_option("-s","--size", dest="size",help="how wide should the spiral be?  (default=3)", metavar="SIZE", type="int")
    
    (options, args) = parser.parse_args()
    
    if( type(options.size) != int ):
        parser.error('Size must be an integer')
    
    for i in spiral(options.size):
        print i