Fix errorbar property cycling to match plot.

QuLogic · QuLogic · commit 149e7fbf2815 · 2020-08-18T23:44:27.000-04:00
It would not cycle if a color were specified. However, this does not match `plot`, which does not advance the cycle only if _all_ properties in the cycle are specified. Notably, this means if your property cycle was for line style, specifying a color would ignore the cycle in `errorbar`, but not in `plot`. Fixes #7074.
diff --git a/doc/api/next_api_changes/behavior/17930-ES.rst b/doc/api/next_api_changes/behavior/17930-ES.rst
@@ -0,0 +1,8 @@
+``Axes.errorbar`` cycles non-color properties correctly
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Formerly, `.Axes.errorbar` incorrectly skipped the Axes property cycle if a
+color was explicitly specified, even if the property cycler was for other
+properties (such as line style). Now, `.Axes.errorbar` will advance the Axes
+property cycle as done for `.Axes.plot`, i.e., as long as all properties in the
+cycler are not explicitly passed.
diff --git a/doc/users/next_whats_new/2020-07-15-errorbar-cycling.rst b/doc/users/next_whats_new/2020-07-15-errorbar-cycling.rst
@@ -0,0 +1,23 @@
+``Axes.errorbar`` cycles non-color properties correctly
+-------------------------------------------------------
+
+Formerly, `.Axes.errorbar` incorrectly skipped the Axes property cycle if a
+color was explicitly specified, even if the property cycler was for other
+properties (such as line style). Now, `.Axes.errorbar` will advance the Axes
+property cycle as done for `.Axes.plot`, i.e., as long as all properties in the
+cycler are not explicitly passed.
+
+For example, the following will cycle through the line styles:
+
+.. plot::
+    :include-source: True
+
+    x = np.arange(0.1, 4, 0.5)
+    y = np.exp(-x)
+    offsets = [0, 1]
+
+    plt.rcParams['axes.prop_cycle'] = plt.cycler('linestyle', ['-', '--'])
+
+    fig, ax = plt.subplots()
+    for offset in offsets:
+        ax.errorbar(x, y + offset, xerr=0.1, yerr=0.3, fmt='tab:blue')
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -3329,13 +3329,10 @@ def errorbar(self, x, y, yerr=None, xerr=None,
             # Remove alpha=0 color that _process_plot_format returns
             fmt_style_kwargs.pop('color')
 
-        if ('color' in kwargs or 'color' in fmt_style_kwargs):
-            base_style = {}
-            if 'color' in kwargs:
-                base_style['color'] = kwargs.pop('color')
-        else:
-            base_style = next(self._get_lines.prop_cycler)
-
+        base_style = self._get_lines._getdefaults(
+            set(), {**fmt_style_kwargs, **kwargs})
+        if 'color' in kwargs:
+            base_style['color'] = kwargs.pop('color')
         base_style['label'] = '_nolegend_'
         base_style.update(fmt_style_kwargs)
         if 'color' not in base_style:
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/errorbar_with_prop_cycle.png b/lib/matplotlib/tests/baseline_images/test_axes/errorbar_with_prop_cycle.png
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -3147,14 +3147,25 @@ def test_errobar_nonefmt():
         assert np.all(errbar.get_color() == mcolors.to_rgba('C0'))
 
 
-@image_comparison(['errorbar_with_prop_cycle.png'],
-                  style='mpl20', remove_text=True)
-def test_errorbar_with_prop_cycle():
-    _cycle = cycler(ls=['--', ':'], marker=['s', 's'], mfc=['k', 'w'])
+@check_figures_equal(extensions=['png'])
+def test_errorbar_with_prop_cycle(fig_test, fig_ref):
+    ax = fig_ref.subplots()
+    ax.errorbar(x=[2, 4, 10], y=[0, 1, 2], yerr=0.5,
+                ls='--', marker='s', mfc='k')
+    ax.errorbar(x=[2, 4, 10], y=[2, 3, 4], yerr=0.5, color='tab:green',
+                ls=':', marker='s', mfc='y')
+    ax.errorbar(x=[2, 4, 10], y=[4, 5, 6], yerr=0.5, fmt='tab:blue',
+                ls='-.', marker='o', mfc='c')
+    ax.set_xlim(1, 11)
+
+    _cycle = cycler(ls=['--', ':', '-.'], marker=['s', 's', 'o'],
+                    mfc=['k', 'y', 'c'], color=['b', 'g', 'r'])
     plt.rc("axes", prop_cycle=_cycle)
-    fig, ax = plt.subplots()
-    ax.errorbar(x=[2, 4, 10], y=[3, 2, 4], yerr=0.5)
-    ax.errorbar(x=[2, 4, 10], y=[6, 4, 2], yerr=0.5)
+    ax = fig_test.subplots()
+    ax.errorbar(x=[2, 4, 10], y=[0, 1, 2], yerr=0.5)
+    ax.errorbar(x=[2, 4, 10], y=[2, 3, 4], yerr=0.5, color='tab:green')
+    ax.errorbar(x=[2, 4, 10], y=[4, 5, 6], yerr=0.5, fmt='tab:blue')
+    ax.set_xlim(1, 11)
 
 
 @check_figures_equal()
