Merge pull request matplotlib#27850 from rcomer/plot_date

Deprecate `plot_date`

Author: dstansby

doc/api/next_api_changes/deprecations/27850-REC.rst

@@ -0,0 +1,10 @@
+``plot_date``
+~~~~~~~~~~~~~
+
+Use of `~.Axes.plot_date` has been discouraged since Matplotlib 3.5 and the
+function is now formally deprecated.
+
+- ``datetime``-like data should directly be plotted using `~.Axes.plot`.
+-  If you need to plot plain numeric data as :ref:`date-format` or need to set
+   a timezone, call ``ax.xaxis.axis_date`` / ``ax.yaxis.axis_date`` before
+   `~.Axes.plot`. See `.Axis.axis_date`.

lib/matplotlib/axes/_axes.py

@@ -1742,17 +1742,17 @@ def plot(self, *args, scalex=True, scaley=True, data=None, **kwargs):
             self._request_autoscale_view("y")
         return lines
 
+    @_api.deprecated("3.9", alternative="plot")
     @_preprocess_data(replace_names=["x", "y"], label_namer="y")
     @_docstring.dedent_interpd
     def plot_date(self, x, y, fmt='o', tz=None, xdate=True, ydate=False,
                   **kwargs):
         """
-        [*Discouraged*] Plot coercing the axis to treat floats as dates.
+        Plot coercing the axis to treat floats as dates.
 
-        .. admonition:: Discouraged
+        .. deprecated:: 3.9
 
-            This method exists for historic reasons and will be deprecated in
-            the future.
+            This method exists for historic reasons and will be removed in version 3.11.
 
             - ``datetime``-like data should directly be plotted using
               `~.Axes.plot`.

lib/matplotlib/tests/test_axes.py

@@ -870,7 +870,8 @@ def test_single_date():
     data1 = [-65.54]
 
     fig, ax = plt.subplots(2, 1)
-    ax[0].plot_date(time1 + dt, data1, 'o', color='r')
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        ax[0].plot_date(time1 + dt, data1, 'o', color='r')
     ax[1].plot(time1, data1, 'o', color='r')
 
 
@@ -6897,11 +6898,13 @@ def test_date_timezone_x():
     # Same Timezone
     plt.figure(figsize=(20, 12))
     plt.subplot(2, 1, 1)
-    plt.plot_date(time_index, [3] * 3, tz='Canada/Eastern')
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        plt.plot_date(time_index, [3] * 3, tz='Canada/Eastern')
 
     # Different Timezone
     plt.subplot(2, 1, 2)
-    plt.plot_date(time_index, [3] * 3, tz='UTC')
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        plt.plot_date(time_index, [3] * 3, tz='UTC')
 
 
 @image_comparison(['date_timezone_y.png'])
@@ -6914,12 +6917,13 @@ def test_date_timezone_y():
     # Same Timezone
     plt.figure(figsize=(20, 12))
     plt.subplot(2, 1, 1)
-    plt.plot_date([3] * 3,
-                  time_index, tz='Canada/Eastern', xdate=False, ydate=True)
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        plt.plot_date([3] * 3, time_index, tz='Canada/Eastern', xdate=False, ydate=True)
 
     # Different Timezone
     plt.subplot(2, 1, 2)
-    plt.plot_date([3] * 3, time_index, tz='UTC', xdate=False, ydate=True)
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        plt.plot_date([3] * 3, time_index, tz='UTC', xdate=False, ydate=True)
 
 
 @image_comparison(['date_timezone_x_and_y.png'], tol=1.0)
@@ -6932,11 +6936,13 @@ def test_date_timezone_x_and_y():
     # Same Timezone
     plt.figure(figsize=(20, 12))
     plt.subplot(2, 1, 1)
-    plt.plot_date(time_index, time_index, tz='UTC', ydate=True)
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        plt.plot_date(time_index, time_index, tz='UTC', ydate=True)
 
     # Different Timezone
     plt.subplot(2, 1, 2)
-    plt.plot_date(time_index, time_index, tz='US/Eastern', ydate=True)
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        plt.plot_date(time_index, time_index, tz='US/Eastern', ydate=True)
 
 
 @image_comparison(['axisbelow.png'], remove_text=True)

lib/matplotlib/tests/test_datetime.py

@@ -657,9 +657,10 @@ def test_plot_date(self):
         x_ranges = np.array(range(1, range_threshold))
         y_ranges = np.array(range(1, range_threshold))
 
-        ax1.plot_date(x_dates, y_dates)
-        ax2.plot_date(x_dates, y_ranges)
-        ax3.plot_date(x_ranges, y_dates)
+        with pytest.warns(mpl.MatplotlibDeprecationWarning):
+            ax1.plot_date(x_dates, y_dates)
+            ax2.plot_date(x_dates, y_ranges)
+            ax3.plot_date(x_ranges, y_dates)
 
     @pytest.mark.xfail(reason="Test for quiver not written yet")
     @mpl.style.context("default")

lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py

@@ -93,7 +93,8 @@ def test_twin_axes_empty_and_removed():
 
 def test_twin_axes_both_with_units():
     host = host_subplot(111)
-    host.plot_date([0, 1, 2], [0, 1, 2], xdate=False, ydate=True)
+    with pytest.warns(mpl.MatplotlibDeprecationWarning):
+        host.plot_date([0, 1, 2], [0, 1, 2], xdate=False, ydate=True)
     twin = host.twinx()
     twin.plot(["a", "b", "c"])
     assert host.get_yticklabels()[0].get_text() == "00:00:00"