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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def convert_svg(svgstr, size, filepath, target):
   "convert to PDF or PNG"
   
   # PREPARE CONVERSION PER TYPE
   if target == "PDF":
      img = cairo.PDFSurface(filepath, size, size)
   
   elif target == "PNG":
      img = cairo.ImageSurface(cairo.FORMAT_ARGB32, size, size)
  
   else:
      system.exit("unknown file type conversion")

   # PROCESS
   ctx = cairo.Context(img)
   handler= rsvg.Handle(None, svgstr)
   iw,ih, fw,fh =  handler.get_dimension_data()
   ctx.translate(0,0)
   ctx.scale(size/fw, size/fh) # assumes bigger source SVG template
   handler.render_cairo(ctx)

   # FINALIZE PER TYPE
   if target == "PNG":
      img.write_to_png(filepath)