Bug summary

When creating a colorbar using a ScalarMappable with the NoNorm normalization and a discrete colormap (e.g., viridis with a fixed number of colors), the ticks returned by the colorbar’s get_ticks() method do not align with the visually displayed tick positions. This will cause cbar.set_ticks(cbar.get_ticks()) to change the ticks.

Code for reproduction

import matplotlib.pyplot as plt
from matplotlib import cm, colors
data = [1, 2, 3, 4, 5]
fig, ax = plt.subplots()
cbar = fig.colorbar(cm.ScalarMappable(norm=colors.NoNorm(), cmap=plt.get_cmap("viridis", len(data))), ax=ax)
print(cbar.get_ticks())
cbar.set_ticks(cbar.get_ticks()) # this unexpectedly changes the ticks

Actual outcome

[0. 1. 2. 3. 4. 5.]

Expected outcome

[0. 1. 2. 3. 4.]

Additional information

No response

Operating system

No response

Matplotlib Version

3.10.8

Matplotlib Backend

No response

Python version

No response

Jupyter version

No response

Installation

None