[Bug]: Incorrect X-axis scaling with date values

Bug summary

In matplotlib 3.9.0, when plotting dates on the X-axis, calling axhspan unexpectedly expands the X-axis range from 1970 to 2024. This behavior did not occur in version 3.8.4, where the X-axis correctly ranges from 2020 to 2024.

Code for reproduction

import datetime
import matplotlib.pyplot as plt

x = [datetime.date(year, 1, 1) for year in range(2020, 2024)]
y = range(4)

plt.plot(x, y)
plt.axhspan(1, 2)

Actual outcome

Expected outcome

Additional information

No response

Operating system

Fedora

Matplotlib Version

3.9.0

Matplotlib Backend

inline or Agg

Python version

3.12.3

Jupyter version

4.2.1

Installation

pip

This is a regression in 3.9.

Most likely related to #26788

@anntzer

A bisect does indeed point to that commit; I'm a bit confused though as it seems like that change is supposed to try and avoid changing the datalimits, but maybe it's something to do with using date/units.

cc @anntzer

Woops. The fix is easy:

diff --git i/lib/matplotlib/axes/_axes.py w/lib/matplotlib/axes/_axes.py
index 9a2b367fb5..7efbd6562f 100644
--- i/lib/matplotlib/axes/_axes.py
+++ w/lib/matplotlib/axes/_axes.py
@@ -1028,7 +1028,7 @@ class Axes(_AxesBase):
         # For Rectangles and non-separable transforms, add_patch can be buggy
         # and update the x limits even though it shouldn't do so for an
         # yaxis_transformed patch, so undo that update.
-        ix = self.dataLim.intervalx
+        ix = self.dataLim.intervalx.copy()
         mx = self.dataLim.minposx
         self.add_patch(p)
         self.dataLim.intervalx = ix

(intervalx is an array and thus vulnerable to getting mutated in place). Note that axvspan already has the necessary copy() call, only axhspan was missing it.
Can you take over the patch?

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[Bug]: Incorrect X-axis scaling with date values #28341

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[Bug]: Incorrect X-axis scaling with date values #28341

Description

Bug summary

Code for reproduction

Actual outcome

Expected outcome

Additional information

Operating system

Matplotlib Version

Matplotlib Backend

Python version

Jupyter version

Installation

Activity

timhoffm commented on Jun 4, 2024

ksunden commented on Jun 4, 2024

QuLogic commented on Jun 4, 2024

anntzer commented on Jun 5, 2024

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