I'm looking for an easy-to-use graphics lib for python that can output to screen as well as pdf. So, I would use code to draw some stuff (simple prims like ovals, rectangles, lines and points) to screen and then when things look good, have it output to pdf.
If you use Tkinter, you can draw on a Canvas widget, then use its .postscript method to save the contents as a PostScript file, which you can convert to PDF using ps2pdf.

postscript(self, cnf={}, **kw)
  Print the contents of the canvas to a postscript
  file. Valid options: colormap, colormode, file, fontmap,
  height, pageanchor, pageheight, pagewidth, pagex, pagey,
  rotate, witdh, x, y.
Recommendations for a simple 2D graphics python library that can output to screen and pdf?