colors has no field TwoSlopeNorm #581

Hi everyone,

It appears that "colors" function imported from matplotlib does not have "Normalize" or "TwoSlopeNorm" field.
Any idea about this?

using PyPlot
vmin, vmax = -1, 1
norm = colors.TwoSlopeNorm(vmin=vmin, vcenter=0., vmax=vmax)

ERROR: type #colors has no field TwoSlopeNorm

Anyways, my goal is to set the colorbar zero at center with symmetric color range.

pcolormesh(data, cmap="RdBu_r", norm = norm, shading="auto")
Colorbar()