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[TST] Added test_arrow in test_datetime.py #27372

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[TST] Added test_arrow in test_datetime.py #27372

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56 changes: 53 additions & 3 deletions lib/matplotlib/tests/test_datetime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -20,11 +20,61 @@ def test_annotate(self):
fig, ax = plt.subplots()
ax.annotate(...)

@pytest.mark.xfail(reason="Test for arrow not written yet")
@mpl.style.context("default")
def test_arrow(self):
fig, ax = plt.subplots()
ax.arrow(...)
mpl.rcParams["date.converter"] = 'concise'
fig, (ax1, ax2, ax3) = plt.subplots(3, 1,
constrained_layout=True,
figsize=(10, 12))

start_date = datetime.datetime(2023, 1, 1)
dates = [start_date + datetime.timedelta(days=i) for i in range(31)]
y_values = range(31)

ax1.plot(dates, y_values, marker='o')
ax1.arrow(x=dates[10],
y=10,
dx=10,
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I would expect the d[xy] values that are used on date-based axes to be timedelta rather than raw numbers (and in particular if it doesn't work that is something we should look at)

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@samchan2022 samchan2022 Nov 29, 2023 •
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Thanks for your review. Unfortunately, currently the function ax.arrow expects the dx, dy to be in the axis units only. We have discovered another issue while implementing datetime test.
Looks like this PR would be blocked meanwhile.

I have tested a minimal change here to get the timedelta working when dx=datetime.timedelta(days=10) with the following patch.
New unitless d[xy] are computed before passing down to the function mpatches.FancyArrow. The drawback is that we now need to import datetime object dependence into the lib/matplotlib/axes/_axes.py. Would be appreciated if you would suggest a better approach to implement the d[xy] timedelta support.

diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 2136ecb2eb..780e5048e0 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -3,6 +3,7 @@ import itertools
 import logging
 import math
 from numbers import Integral, Number, Real
+import datetime
 
 import numpy as np
 from numpy import ma
@@ -5218,13 +5219,22 @@ default: :rc:`scatter.edgecolors`
         ...             arrowprops=dict(arrowstyle="->"))
 
         """
+        old_x=x
+        old_y=y
         # Strip away units for the underlying patch since units
         # do not make sense to most patch-like code
         x = self.convert_xunits(x)
         y = self.convert_yunits(y)
-        dx = self.convert_xunits(dx)
-        dy = self.convert_yunits(dy)
-
+        # if dx is timedelta, compute the unitless dx after convert
+        if isinstance(dx, datetime.timedelta):
+            dx = self.convert_xunits( old_x + dx ) - x
+        else:
+            dx = self.convert_xunits(dx)
+        # if dy is timedelta, compute the unitless dy after convert
+        if isinstance(dy, datetime.timedelta):
+            dy = self.convert_xunits( old_y + dy ) - y
+        else:
+            dy = self.convert_yunits(dy)
         a = mpatches.FancyArrow(x, y, dx, dy, **kwargs)
         self.add_patch(a)
         self._request_autoscale_view()

dy=10,
head_width=1,
head_length=1,
linewidth=3,
facecolor='red',
edgecolor='red',
transform=ax1.transData)
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specifying the transform as transData is not necessary, as that is the default.

ax1.set_title('Datetime vs. Number')
ax1.set_xlabel('Date')
ax1.set_ylabel('Number')

ax2.plot(y_values, dates, marker='o')
ax2.arrow(x=10,
y=dates[10],
dx=10,
dy=10,
head_width=1,
head_length=1,
linewidth=3,
facecolor='red',
edgecolor='red',
transform=ax2.transData)
ax2.set_title('Number vs. Datetime')
ax2.set_xlabel('Number')
ax2.set_ylabel('Date')

ax3.plot(dates, dates, marker='o')
ax3.arrow(x=dates[10],
y=dates[10],
dx=10,
dy=10,
head_width=1,
head_length=1,
linewidth=3,
facecolor='red',
edgecolor='red',
transform=ax3.transData)
ax3.set_title('Datetime vs. Datetime')
ax3.set_xlabel('Date')
ax3.set_ylabel('Date')

@mpl.style.context("default")
def test_axhline(self):
Expand Down