matplotlib · timhoffm · Aug 19, 2020 · Jul 15, 2020 · Jul 18, 2020 · Jul 18, 2020
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
@@ -3315,35 +3315,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
 
         self._process_unit_info(xdata=x, ydata=y, kwargs=kwargs)
 
-        plot_line = (fmt.lower() != 'none')
-        label = kwargs.pop("label", None)
-
-        if fmt == '':
-            fmt_style_kwargs = {}
-        else:
-            fmt_style_kwargs = {k: v for k, v in
-                                zip(('linestyle', 'marker', 'color'),
-                                    _process_plot_format(fmt))
-                                if v is not None}
-        if fmt == '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['label'] = '_nolegend_'
-        base_style.update(fmt_style_kwargs)
-        if 'color' not in base_style:
-            base_style['color'] = 'C0'
-        if ecolor is None:
-            ecolor = base_style['color']
-        # make sure all the args are iterable; use lists not arrays to
-        # preserve units
+        # Make sure all the args are iterable; use lists not arrays to preserve
+        # units.
         if not np.iterable(x):
             x = [x]
 
@@ -3361,19 +3334,50 @@ def errorbar(self, x, y, yerr=None, xerr=None,
             if not np.iterable(yerr):
                 yerr = [yerr] * len(y)
 
-        # make the style dict for the 'normal' plot line
-        plot_line_style = {
-            **base_style,
-            **kwargs,
-            'zorder': (kwargs['zorder'] - .1 if barsabove else
-                       kwargs['zorder'] + .1),
-        }
+        label = kwargs.pop("label", None)
+        kwargs['label'] = '_nolegend_'
+
+        # Create the main line and determine overall kwargs for child artists.
+        # We avoid calling self.plot() directly, or self._get_lines(), because
+        # that would call self._process_unit_info again, and do other indirect
+        # data processing.
+        (data_line, base_style), = self._get_lines._plot_args(
+            (x, y) if fmt == '' else (x, y, fmt), kwargs, return_kwargs=True)
+
+        # Do this after creating `data_line` to avoid modifying `base_style`.
+        if barsabove:
+            data_line.set_zorder(kwargs['zorder'] - .1)
+        else:
+            data_line.set_zorder(kwargs['zorder'] + .1)
+
+        # Add line to plot, or throw it away and use it to determine kwargs.
+        if fmt.lower() != 'none':
+            self.add_line(data_line)
+        else:
+            data_line = None
+            # Remove alpha=0 color that _get_lines._plot_args returns for
+            # 'none' format, and replace it with user-specified color, if
+            # supplied.
+            base_style.pop('color')
+            if 'color' in kwargs:
+                base_style['color'] = kwargs.pop('color')
+
+        if 'color' not in base_style:
+            base_style['color'] = 'C0'
+        if ecolor is None:
+            ecolor = base_style['color']
 
-        # make the style dict for the line collections (the bars)
-        eb_lines_style = dict(base_style)
-        eb_lines_style.pop('marker', None)
-        eb_lines_style.pop('linestyle', None)
-        eb_lines_style['color'] = ecolor
+        # Eject any marker information from line format string, as it's not
+        # needed for bars or caps.
+        base_style.pop('marker', None)
+        base_style.pop('markersize', None)
+        base_style.pop('markerfacecolor', None)
+        base_style.pop('markeredgewidth', None)
+        base_style.pop('markeredgecolor', None)
+        base_style.pop('linestyle', None)
+
+        # Make the style dict for the line collections (the bars).
+        eb_lines_style = {**base_style, 'color': ecolor}
 
         if elinewidth:
             eb_lines_style['linewidth'] = elinewidth
@@ -3384,15 +3388,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
             if key in kwargs:
                 eb_lines_style[key] = kwargs[key]
 
-        # set up cap style dictionary
-        eb_cap_style = dict(base_style)
-        # eject any marker information from format string
-        eb_cap_style.pop('marker', None)
-        eb_lines_style.pop('markerfacecolor', None)
-        eb_lines_style.pop('markeredgewidth', None)
-        eb_lines_style.pop('markeredgecolor', None)
-        eb_cap_style.pop('ls', None)
-        eb_cap_style['linestyle'] = 'none'
+        # Make the style dict for the caps.
+        eb_cap_style = {**base_style, 'linestyle': 'none'}
         if capsize is None:
             capsize = rcParams["errorbar.capsize"]
         if capsize > 0:
@@ -3408,11 +3405,6 @@ def errorbar(self, x, y, yerr=None, xerr=None,
                 eb_cap_style[key] = kwargs[key]
         eb_cap_style['color'] = ecolor
 
-        data_line = None
-        if plot_line:
-            data_line = mlines.Line2D(x, y, **plot_line_style)
-            self.add_line(data_line)
-
         barcols = []
         caplines = []
 

diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -310,7 +310,7 @@ def _makeline(self, x, y, kw, kwargs):
         default_dict = self._getdefaults(set(), kw)
         self._setdefaults(default_dict, kw)
         seg = mlines.Line2D(x, y, **kw)
-        return seg
+        return seg, kw
 
     def _makefill(self, x, y, kw, kwargs):
         # Polygon doesn't directly support unitized inputs.
@@ -362,9 +362,9 @@ def _makefill(self, x, y, kw, kwargs):
                                fill=kwargs.get('fill', True),
                                closed=kw['closed'])
         seg.set(**kwargs)
-        return seg
+        return seg, kwargs
 
-    def _plot_args(self, tup, kwargs):
+    def _plot_args(self, tup, kwargs, return_kwargs=False):
         if len(tup) > 1 and isinstance(tup[-1], str):
             linestyle, marker, color = _process_plot_format(tup[-1])
             tup = tup[:-1]
@@ -415,8 +415,12 @@ def _plot_args(self, tup, kwargs):
         ncx, ncy = x.shape[1], y.shape[1]
         if ncx > 1 and ncy > 1 and ncx != ncy:
             raise ValueError(f"x has {ncx} columns but y has {ncy} columns")
-        return [func(x[:, j % ncx], y[:, j % ncy], kw, kwargs)
-                for j in range(max(ncx, ncy))]
+        result = (func(x[:, j % ncx], y[:, j % ncy], kw, kwargs)
+                  for j in range(max(ncx, ncy)))
+        if return_kwargs:
+            return list(result)
+        else:
+            return [l[0] for l in result]
 
 
 @cbook._define_aliases({"facecolor": ["fc"]})

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()