PR Summary

As noted in issue #11510, extra ticks can get into the colorbar that extend past the minimum or maximum due to the presence of the "extend='both/lower/upper'` kwarg. This fixes that issue for major ticks.

An enhancement would be to come up with a cb.minorticks_on function to colorbar that supplies the appropriately trimmed minor tick locator as well. That can be a further PR. But this really fixes a bug in the existing functionality...

import matplotlib.pyplot as plt
import numpy as np

np.random.seed(seed=12345)
x = np.random.randn(20, 20)
fig, ax = plt.subplots()
im = ax.pcolormesh(x)

cbar = fig.colorbar(im, extend='both')
plt.show()

Before:

After

PR Checklist

• Has Pytest style unit tests
• Code is PEP 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way