"""
 svg_graph.py

 Create an SVG version of a graph, e.g.

 <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
 "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
 <svg width="100%" height="100%" version="1.1" xmlns="http://www.w3.org/2000/svg">
  <line x1="30.000000" y1="40.000000" x2="80.000000" y2="95.000000"
      style="stroke:grey;stroke-width:1.000000"/>
  <line x1="80.000000" y1="95.000000" x2="200.000000" y2="250.000000"
      style="stroke:grey;stroke-width:1.000000"/>
  <circle cx="30.000000" cy="40.000000" r="5.000000"
      style="stroke:black;stroke-width:1;fill:red" />
  <circle cx="80.000000" cy="95.000000" r="5.000000"
      style="stroke:black;stroke-width:1;fill:red" />
  <circle cx="200.000000" cy="250.000000" r="5.000000"
      style="stroke:black;stroke-width:1;fill:red" />
  <text x="35.000000" y="35.000000"
      style="font-family:Verdana;font-size:12">Boston</text>
  <text x="85.000000" y="90.000000"
      style="font-family:Verdana;font-size:12">Chicago</text>
  <text x="205.000000" y="245.000000"
      style="font-family:Verdana;font-size:12">New York</text>
 </svg>

 with python code like this.

   from svg_graph import SvgGraph
   SvgGraph()\
    .line(30, 40, 80, 95) \
    .line(80, 95, 200, 250) \
    .dot(30, 40) \
    .dot(80, 95) \
    .dot(200, 250) \
    .text("Boston", 35, 35) \
    .text("Chicago", 85, 90) \
    .text("New York", 205, 245) \
    .write("svgtest")

Jim Mahoney | MIT License | Dec 2010
"""

svg_header = """<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg width="100%" height="100%" version="1.1" xmlns="http://www.w3.org/2000/svg">
"""

svg_footer = """</svg>
"""

class SvgGraph(object):
  def __init__(self, scale=1.0):
    self.scale = scale
    self.xml = ""
  def write(self, filename="graph"):
    """ Write the given xml to a file; default name is 'graph.svg'. """
    if not filename.endswith('.svg'):
      filename += '.svg'
    svg_file = open(filename, 'w')
    svg_file.write(self.header())
    svg_file.write(self.xml)
    svg_file.write(self.footer())
    svg_file.close()
  def window_coords(self, *xy):
    return map(lambda z: self.scale * z, xy)
  def header(self):
    return svg_header
  def footer(self):
    return svg_footer
  def line(self, x1, y1, x2, y2, color='grey', width=1):
    (x1, y1, x2, y2) = self.window_coords(x1, y1, x2, y2)
    self.xml += ("""  <line x1="%f" y1="%f" x2="%f" y2="%f"\n""" + \
           """      style="stroke:%s;stroke-width:%f"/>\n""") % \
           (x1, y1, x2, y2, color, width)
    return self
  def dot(self, x, y, color='red', radius=5):
    (x, y) = self.window_coords(x, y)
    self.xml += ("""  <circle cx="%f" cy="%f" r="%f"\n""" + \
           """      style="stroke:black;stroke-width:1;fill:%s" />\n""") % \
           (x, y, radius, color)
    return self
  def text(self, string, x, y):
    (x, y) = self.window_coords(x, y)
    self.xml += ("""  <text x="%f" y="%f"\n""" + \
           """      style="font-family:Verdana;font-size:12">%s</text>\n""") % \
           (x, y, string)
    return self