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I've always found the third colorbar example from the gallery quite inelegant (http://matplotlib.org/examples/api/colorbar_only.html). Very often, you would like to extend your colorbar while using the same color scheme as the current colormap, not by adding new colors with set_over and set_under.
Maybe I am missing something, but the current behaviour without set_over leads to the same color for the last box of the colorbar and the extension. I found it quite easy to add a new extend keyword to the existing BoundaryNorm class that does the exact same thing as before but handles the color choice differently. It is best shown with the example below:
import matplotlib as mpl
from matplotlib import pyplot
fig = pyplot.figure(figsize=(8,3))
ax1 = fig.add_axes([0.05, 0.80, 0.9, 0.15])
ax2 = fig.add_axes([0.05, 0.475, 0.9, 0.15])
ax3 = fig.add_axes([0.05, 0.15, 0.9, 0.15])
bounds = [-1, 2, 5, 7, 12, 15]
cmap = mpl.cm.get_cmap('jet')
# Default behavior
norm = mpl.colors.BoundaryNorm(bounds, cmap.N)
cb1 = mpl.colorbar.ColorbarBase(ax1, cmap=cmap,
norm=norm,
extend='both',
orientation='horizontal')
cb1.set_label('Default BoundaryNorm ouput');
# With the new keyword
norm = mpl.colors.BoundaryNorm(bounds, cmap.N, extend='both')
cb2 = mpl.colorbar.ColorbarBase(ax2, cmap=cmap,
norm=norm,
# Ideally this keyword could
# be omitted since it is redundant
extend='both',
orientation='horizontal')
cb2.set_label('With the new keyword');
# Just max
norm = mpl.colors.BoundaryNorm(bounds, cmap.N, extend='max')
cb3 = mpl.colorbar.ColorbarBase(ax3, cmap=cmap,
norm=norm,
extend='max',
orientation='horizontal')
cb3.set_label('Just max');Which produces:
What do you think? If accepted I could easily add it to my ongoing PR
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