Pyplot: vertical gradient fill under curve?

Question

I'm wondering if there's a way to fill under a pyplot curve with a vertical gradient, like in this quick mockup:

I found this hack on StackOverflow, and I don't mind the polygons if I could figure out how to make the color map vertical: How to fill rainbow color under a curve in Python matplotlib

Answer 1

There is an alternative solution closer to the sketch in the question. It's given on Henry Barthes' blog http://pradhanphy.blogspot.com/2014/06/filling-between-curves-with-color.html. This applies an imshow to each of the patches, I've copied the code in case the link changes,

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.path import Path
from matplotlib.patches import PathPatch

xx=np.arange(0,10,0.01)
yy=xx*np.exp(-xx)

path = Path(np.array([xx,yy]).transpose())
patch = PathPatch(path, facecolor='none')
plt.gca().add_patch(patch)

im = plt.imshow(xx.reshape(yy.size,1),   
                cmap=plt.cm.Reds,
                interpolation="bicubic",
                origin='lower',
                extent=[0,10,-0.0,0.40],
                aspect="auto",
                clip_path=patch, 
                clip_on=True)
plt.show()

Answer 2

There may be a better way, but here goes:

from matplotlib import pyplot as plt

x = range(10)
y = range(10)
z = [[z] * 10 for z in range(10)]
num_bars = 100  # more bars = smoother gradient

plt.contourf(x, y, z, num_bars)

background_color = 'w'
plt.fill_between(x, y, y2=max(y), color=background_color)

plt.show()

Shows: