matplotlib, set color of lines along a grayscale using numbers from 0. (white) to 1. (black)

Question

I've been trying to follow the instructions here to set the color of many lines along a grayscale using floats from 0. (white) to 1. (black). The function line.set_color() accepts the floats, but the error below appears when I do plt.show():

ValueError: to_rgba: Invalid rgba arg "1.0"
to_rgb: Invalid rgb arg "1.0"
cannot convert argument to rgb sequence

In this answer it is explained how to do that using plt.cm.RdYlBu(i). Is there any equivalent for grayscale?

Answer 1

For historical reasons, matplotlib expects "floats" to be interpreted as grayscale values to be passed in as strings, which is the reason for your error.

For example:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot(range(10), color="0.5")
plt.show()

Also, for a grayscale colormap, just use plt.cm.gray or plt.cm.gray_r (reversed). There's a full list of colormaps here: http://matplotlib.org/examples/pylab_examples/show_colormaps.html