PyX — Example: graphstyles/changesymbol.py

import random
from pyx import *

# introduce a new symbol style where size and color are given by some data
class changesymbol(graph.style.symbol):

    def __init__(self, sizecolumnname="size", colorcolumnname="color",
                       gradient=color.gradient.Rainbow,
                       symbol=graph.style.symbol.circle,
                       symbolattrs=[deco.filled, deco.stroked([color.gray.black])],
                       **kwargs):
        # add some configuration parameters and modify some other
        self.sizecolumnname = sizecolumnname
        self.colorcolumnname = colorcolumnname
        self.gradient = gradient
        graph.style.symbol.__init__(self, symbol=symbol, symbolattrs=symbolattrs, **kwargs)

    def columnnames(self, privatedata, sharedata, agraph, columnnames, dataaxisnames):
        # register the new column names
        if self.sizecolumnname not in columnnames:
            raise ValueError("column '%s' missing" % self.sizecolumnname)
        if self.colorcolumnname not in columnnames:
            raise ValueError("column '%s' missing" % self.colorcolumnname)
        return ([self.sizecolumnname, self.colorcolumnname] +
                graph.style.symbol.columnnames(self, privatedata, sharedata, agraph,
                                               columnnames, dataaxisnames))

    def drawpoint(self, privatedata, sharedata, graph, point):
        # replace the original drawpoint method by a slightly revised one
        if sharedata.vposvalid and privatedata.symbolattrs is not None:
            x_pt, y_pt = graph.vpos_pt(*sharedata.vpos)
            color = self.gradient.getcolor(point[self.colorcolumnname])
            privatedata.symbol(privatedata.symbolcanvas, x_pt, y_pt,
                               privatedata.size_pt*point[self.sizecolumnname],
                               privatedata.symbolattrs + [color])

g = graph.graphxy(width=10)
g.plot(graph.data.points([[random.random() for i in range(4)]
                          for i in range(1000)],
                         x=1, y=2, size=3, color=4),
       [changesymbol()])
g.writeEPSfile("changesymbol")
g.writePDFfile("changesymbol")
g.writeSVGfile("changesymbol")