>>> """
===============
SVG Filter Line
===============

Demonstrate SVG filtering effects which might be used with Matplotlib.

Note that the filtering effects are only effective if your SVG renderer
support it.
"""
... 
... import io
... import xml.etree.ElementTree as ET
... 
... import matplotlib.pyplot as plt
... import matplotlib.transforms as mtransforms
... 
... fig1 = plt.figure()
... ax = fig1.add_axes([0.1, 0.1, 0.8, 0.8])
... 
... # draw lines
... l1, = ax.plot([0.1, 0.5, 0.9], [0.1, 0.9, 0.5], "bo-",
...               mec="b", lw=5, ms=10, label="Line 1")
... l2, = ax.plot([0.1, 0.5, 0.9], [0.5, 0.2, 0.7], "rs-",
...               mec="r", lw=5, ms=10, label="Line 2")
... 
... 
... for l in [l1, l2]:
... 
...     # draw shadows with same lines with slight offset and gray colors.
... 
...     xx = l.get_xdata()
...     yy = l.get_ydata()
...     shadow, = ax.plot(xx, yy)
...     shadow.update_from(l)
... 
...     # adjust color
...     shadow.set_color("0.2")
...     # adjust zorder of the shadow lines so that it is drawn below the
...     # original lines
...     shadow.set_zorder(l.get_zorder() - 0.5)
... 
...     # offset transform
...     ot = mtransforms.offset_copy(l.get_transform(), fig1,
...                                  x=4.0, y=-6.0, units='points')
... 
...     shadow.set_transform(ot)
... 
...     # set the id for a later use
...     shadow.set_gid(l.get_label() + "_shadow")
... 
... 
... ax.set_xlim(0., 1.)
... ax.set_ylim(0., 1.)
... 
... # save the figure as a bytes string in the svg format.
... f = io.BytesIO()
... plt.savefig(f, format="svg")
... 
... 
... # filter definition for a gaussian blur
... filter_def = """
...   <defs xmlns='http://www.w3.org/2000/svg'
...         xmlns:xlink='http://www.w3.org/1999/xlink'>
...     <filter id='dropshadow' height='1.2' width='1.2'>
...       <feGaussianBlur result='blur' stdDeviation='3'/>
...     </filter>
...   </defs>
... """
... 
... 
... # read in the saved svg
... tree, xmlid = ET.XMLID(f.getvalue())
... 
... # insert the filter definition in the svg dom tree.
... tree.insert(0, ET.XML(filter_def))
... 
... for l in [l1, l2]:
...     # pick up the svg element with given id
...     shadow = xmlid[l.get_label() + "_shadow"]
...     # apply shadow filter
...     shadow.set("filter", 'url(#dropshadow)')
... 
... fn = "svg_filter_line.svg"
... print(f"Saving '{fn}'")
... ET.ElementTree(tree).write(fn)
...