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For fixed custom x-axis labels in Matplotlib, pair each label with its position using ax.set_xticks(positions, labels). The older ax.set_xticklabels() method is discouraged in the current Matplotlib 3.11.2 documentation because labels can become detached from tick positions.
Set custom labels and positions together
Use Axes.set_xticks(positions, labels) when a plot needs specific category names at known x coordinates. Each label stays paired with its intended position:
import matplotlib.pyplot as plt
values = [12, 18, 9]
positions = [0, 1, 2]
labels = ["North", "Central", "South"]
fig, ax = plt.subplots()
ax.bar(positions, values)
ax.set_xticks(positions, labels)
ax.set_xlabel("Region")
fig.tight_layout()
plt.show()This is the recommended approach in the Matplotlib Axes API. It is suited to a final plot with deliberate, fixed categories. Fixed ticks do not necessarily adapt when users pan or zoom; for interactive plots, use a locator and formatter that can respond to changing ticks.
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Use set_xticklabels only when you have fixed the ticks
Axes.set_xticklabels() is discouraged because it depends on tick positions. If you are updating existing code that uses it, set the positions first, then provide exactly one label for each position:
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positions = [0, 1, 2]
labels = ["North", "Central", "South"]
ax.set_xticks(positions)
ax.set_xticklabels(labels)The labels are applied in tick order, not matched to numeric x values. Under the hood, set_xticklabels uses a FixedFormatter, which should be paired with a FixedLocator so the tick locations stay fixed. The Axis.set_ticklabels API documents the method’s limitations and the requirement that the label count match the tick locations.
Use a formatter when labels come from tick values
If labels should be calculated from whatever tick values Matplotlib chooses, use a formatter rather than a hard-coded list. For example, FuncFormatter can format numeric ticks as currency:
from matplotlib.ticker import FuncFormatter
ax.xaxis.set_major_formatter(
FuncFormatter(lambda x, pos: f"${x:,.0f}")
)The formatter receives the tick value and its position and returns the displayed text. This keeps the label rule tied to the value as the locator selects ticks. The ticker API also documents StrMethodFormatter and specialized date and scale-aware locator/formatter options.
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- Labels appear shifted or change after plotting: Set positions and labels together with
set_xticks(positions, labels), or fix the tick positions before callingset_xticklabels. - The number of labels does not match the number of ticks: Make both sequences the same length, with one label for each tick location.
- Labels should represent values rather than category positions: Use a value-aware formatter such as
FuncFormatterinstead of assigning a fixed list. - Ticks should respond to pan or zoom: Use an automatic locator with a formatter so ticks and labels can adjust to the view.
- You only want to change tick appearance: Prefer
set_tick_paramsfor tick styling. Label keyword arguments toset_xticklabelsaffect current tick objects and may not persist if ticks are regenerated.
See Matplotlib’s Axis ticks guide for more on choosing between fixed ticks and automatic tick behavior.
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