IPython's SVG display functionality, in conjunction with the ease of making SVG strings using ElementTrees, makes it really easy to have a nice drawing canvas inside of IPython.

svg-display.ipynb

{
 "metadata": {
  "name": "svg-display"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": "# Playing with SVG graphics in IPython"
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": "IPython's SVG display functionality, in conjunction with the ease of making SVG strings using ElementTrees, makes it really easy to have a nice drawing canvas inside of IPython."
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "from IPython.display import SVG\n\ndef tosvg(polygons,border=0):\n    \"\"\"\n    Convert a list of polygons into an SVG image.\n    Polygons are lists of x,y tuples.\n    \"\"\"\n    import xml.etree.ElementTree as ET\n\n    colors = ['aqua','blue','fuchsia','gray','green','lime','maroon',\n              'navy','olive','purple','red','silver','teal','yellow']\n\n    xmin,xmax,ymin,ymax = bbox(polygons,border)\n    width = xmax-xmin\n    height = ymax-ymin\n\n    svg = ET.Element('svg', xmlns=\"http://www.w3.org/2000/svg\", version=\"1.1\",\n                    height=\"%s\" % height, width=\"%s\" % width)\n    for i,polygon in enumerate(polygons):\n        point_list = \" \".join([\"%d,%d\" % (x-xmin,y-ymin) for (x,y) in polygon])\n        ET.SubElement(svg,\"polygon\",fill=colors[i%len(colors)],\n                      stroke=\"black\",points=point_list)\n    #ET.dump(svg)\n    return ET.tostring(svg)\n\ndef bbox(polygons,border=0,BIG=1e10):\n    \"\"\"\n    Compute the bounding box of a list of polygons. Border adds an optional\n    border amount to all values in the bbox. \n    \"\"\"\n    xmin=ymin = BIG\n    xmax=ymax = -BIG\n    for polygon in polygons:\n        for x,y in polygon:\n            xmax = max(xmax,x)\n            xmin = min(xmin,x)\n            ymax = max(ymax,y)\n            ymin = min(ymin,y)\n    return xmin-border,xmax+border,ymin-border,ymax+border",
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 2
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": "Given a list of polygons as a list of x,y tuples, you can display them:"
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "polygons = [\n    [(-20,0),(0,100),(5,100),(5,0)],\n    [(1,1),(1,10),(10,10),(10,1)],\n    [(10,10),(10,50),(50,50),(50,10)],\n    [(50,50),(50,150),(150,150),(150,50)],\n    ]\nSVG(tosvg(polygons))",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 3,
       "svg": "<svg height=\"150\" version=\"1.1\" width=\"170\" xmlns=\"http://www.w3.org/2000/svg\"><polygon fill=\"aqua\" points=\"0,0 20,100 25,100 25,0\" stroke=\"black\"/><polygon fill=\"blue\" points=\"21,1 21,10 30,10 30,1\" stroke=\"black\"/><polygon fill=\"fuchsia\" points=\"30,10 30,50 70,50 70,10\" stroke=\"black\"/><polygon fill=\"gray\" points=\"70,50 70,150 170,150 170,50\" stroke=\"black\"/></svg>",
       "text": "<IPython.core.display.SVG at 0x112e66e50>"
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": "and play with the padding:"
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "SVG(tosvg(polygons,100))",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 4,
       "svg": "<svg height=\"350\" version=\"1.1\" width=\"370\" xmlns=\"http://www.w3.org/2000/svg\"><polygon fill=\"aqua\" points=\"100,100 120,200 125,200 125,100\" stroke=\"black\"/><polygon fill=\"blue\" points=\"121,101 121,110 130,110 130,101\" stroke=\"black\"/><polygon fill=\"fuchsia\" points=\"130,110 130,150 170,150 170,110\" stroke=\"black\"/><polygon fill=\"gray\" points=\"170,150 170,250 270,250 270,150\" stroke=\"black\"/></svg>",
       "text": "<IPython.core.display.SVG at 0x112e59c50>"
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": "## Fancier Version\nHere's a fancier version I wrote a long time ago, updated to use _repr_svg_ for automatic display."
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "import xml.etree.ElementTree as ET\n\nclass SVGScene:\n    def __init__(self):\n        self.items = []\n        self.height = 400 # override with bbox calculation\n        self.width = 400 # override with bbox calculation\n        return\n\n    def add(self,item): self.items.append(item)\n        \n    def bbox(self,border=0,BIG=1e10):\n        self.xmin = self.ymin = BIG\n        self.xmax = self.ymax = -BIG\n        for item in self.items:\n            xmin,xmax,ymin,ymax = item.bbox()\n            self.xmin = min(self.xmin,xmin)\n            self.xmax = max(self.xmax,xmax)\n            self.ymin = min(self.ymin,ymin)\n            self.ymax = max(self.ymax,ymax)\n        self.xmin -= border\n        self.ymin -= border\n        self.xmax += border\n        self.ymax += border\n        self.height = self.ymax\n        self.width = self.xmax\n        return\n    \n    def _repr_svg_(self): return self.to_svg()\n    \n    def to_svg(self):\n        self.bbox(10)\n        svg = ET.Element('svg', xmlns=\"http://www.w3.org/2000/svg\", version=\"1.1\",\n                        height=\"%s\" % self.height, width=\"%s\" % self.width)\n        g = ET.SubElement(svg,\"g\",style=\"fill-opacity:1.0; stroke:black; stroke-width:1;\")\n        for item in self.items:\n            item.to_svg(g)\n        #ET.dump(svg) # useful for debugging\n        return ET.tostring(svg)\n\n    def line(self,start,end): self.items.append(Line(start,end))\n    def circle(self,center,radius,color='blue'): self.items.append(Circle(center,radius,color))\n    def rectangle(self,origin,height,width,color='blue'): self.items.append(Rectangle(origin,height,width,color))\n    def text(self,origin,text,size=24): self.items.append(Text(origin,text,size))\n    \nclass Line:\n    def __init__(self,start,end):\n        self.start = start #xy tuple\n        self.end = end     #xy tuple\n        return\n    \n    def to_svg(self,parent):\n        ET.SubElement(parent,\"line\",x1=str(self.start[0]),y1=str(self.start[1]),x2=str(self.end[0]),y2=str(self.end[1]))\n\n    def bbox(self):\n        return min(self.start[0],self.end[0]),max(self.start[0],self.end[0]),min(self.start[1],self.end[1]),max(self.start[1],self.end[1])\n\n\nclass Circle:\n    def __init__(self,center,radius,color):\n        self.center = center #xy tuple\n        self.radius = radius #xy tuple\n        self.color = color   #rgb tuple in range(0,256)\n        return\n    \n    def to_svg(self,parent):\n        color = colorstr(self.color)\n        ET.SubElement(parent,\"circle\",cx=str(self.center[0]),cy=str(self.center[1]),r=str(self.radius),\n                      style=\"fill:%s;\" % color)\n\n    def bbox(self):\n        return self.center[0]-self.radius,self.center[0]+self.radius,self.center[1]-self.radius,self.center[1]+self.radius\n\nclass Rectangle:\n    def __init__(self,origin,height,width,color):\n        self.origin = origin\n        self.height = height\n        self.width = width\n        self.color = color\n        return\n\n    def to_svg(self,parent):\n        color = colorstr(self.color)\n        ET.SubElement(parent,\"rect\",x=str(self.origin[0]),y=str(self.origin[1]),height=str(self.height),\n                      width=str(self.width),style=\"fill:%s;\" % color)\n\n    def bbox(self):\n        return self.origin[0],self.origin[0]+self.width,self.origin[1],self.origin[1]+self.height\n\nclass Text:\n    def __init__(self,origin,text,size=24):\n        self.origin = origin\n        self.text = text\n        self.size = size\n        return\n\n    def to_svg(self,parent):\n        fs = \"font-size\"\n        el = ET.SubElement(parent,\"text\",x=str(self.origin[0]),y=str(self.origin[1]))\n        el.set(\"font-size\",str(self.size))\n        el.text = self.text\n    \n    def bbox(self):\n        return self.origin[0],self.origin[0]+self.size,self.origin[1],self.origin[1]+self.size # Guessing here\n    \ndef colorstr(rgb): \n    if type(rgb) == type(\"\"): return rgb\n    return \"#%x%x%x\" % (rgb[0]/16,rgb[1]/16,rgb[2]/16)",
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 14
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": "For example:"
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "scene = SVGScene()\nscene.rectangle((100,100),200,200,(0,255,255))\nscene.line((200,200),(200,300))\nscene.line((200,200),(300,200))\nscene.line((200,200),(100,200))\nscene.line((200,200),(200,100))\nscene.circle((200,200),30,(0,0,255))\nscene.circle((200,300),30,(0,255,0))\nscene.circle((300,200),30,(255,0,0))\nscene.circle((100,200),30,(255,255,0))\nscene.circle((200,100),30,\"fuchsia\")\nscene.text((50,50),\"Testing SVG\")\nscene",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 15,
       "svg": "<svg height=\"340\" version=\"1.1\" width=\"340\" xmlns=\"http://www.w3.org/2000/svg\"><g style=\"fill-opacity:1.0; stroke:black; stroke-width:1;\"><rect height=\"200\" style=\"fill:#0ff;\" width=\"200\" x=\"100\" y=\"100\" /><line x1=\"200\" x2=\"200\" y1=\"200\" y2=\"300\" /><line x1=\"200\" x2=\"300\" y1=\"200\" y2=\"200\" /><line x1=\"200\" x2=\"100\" y1=\"200\" y2=\"200\" /><line x1=\"200\" x2=\"200\" y1=\"200\" y2=\"100\" /><circle cx=\"200\" cy=\"200\" r=\"30\" style=\"fill:#00f;\" /><circle cx=\"200\" cy=\"300\" r=\"30\" style=\"fill:#0f0;\" /><circle cx=\"300\" cy=\"200\" r=\"30\" style=\"fill:#f00;\" /><circle cx=\"100\" cy=\"200\" r=\"30\" style=\"fill:#ff0;\" /><circle cx=\"200\" cy=\"100\" r=\"30\" style=\"fill:fuchsia;\" /><text font-size=\"24\" x=\"50\" y=\"50\">Testing SVG</text></g></svg>",
       "text": "<__main__.SVGScene instance at 0x1129e6c20>"
      }
     ],
     "prompt_number": 15
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "",
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 6
    }
   ],
   "metadata": {}
  }
 ]
}

may I suggest adding a _repr_svg_ to Scene ?

@Carreau - great idea. Done!

To get it working with Jupyter + Python 3.6 I had to do the following:
return "#%x%x%x" % (int(rgb[0]/16),int(rgb[1]/16),int(rgb[2]/16))
SVG(scene.to_svg())