UserWarning: FixedFormatter should only be used together with FixedLocator

UserWarning: FixedFormatter should only be used together with FixedLocator

$ python -c "import matplotlib.pyplot as plt; ax = plt.axes(); ax.set_xticklabels(['a','b','c'])"
/usr/lib/.../matplotlib/axis.py:...: UserWarning: FixedFormatter should only be used together with FixedLocator

Why this happens

You set tick labels without fixing tick locations.

Fix

Use FixedLocator with FixedFormatter or set ticks via set_xticks and labels via set_xticklabels paired appropriately.

Wrong code

import matplotlib.pyplot as plt
ax = plt.axes()
ax.set_xticklabels(['a','b','c'])

Fixed code

import matplotlib.pyplot as plt
import matplotlib.ticker as mticker
ax = plt.axes()
ax.xaxis.set_major_locator(mticker.FixedLocator([0,1,2]))
ax.xaxis.set_major_formatter(mticker.FixedFormatter(['a','b','c']))