BUG: Ensuring that _get_standard_colors returns num_colors (GH #20585)

doc/source/whatsnew/v0.24.0.rst

@@ -1597,6 +1597,7 @@ Plotting
 
 - Bug in :func:`DataFrame.plot.scatter` and :func:`DataFrame.plot.hexbin` caused x-axis label and ticklabels to disappear when colorbar was on in IPython inline backend (:issue:`10611`, :issue:`10678`, and :issue:`20455`)
 - Bug in plotting a Series with datetimes using :func:`matplotlib.axes.Axes.scatter` (:issue:`22039`)
+- Bug in :func:`DataFrame.plot.bar` caused bars to use multiple colors instead of a single one (:issue:`20585`)
 - Bug in validating color parameter caused extra color to be appended to the given color array. This happened to multiple plotting functions using matplotlib. (:issue:`20726`)
 
 Groupby/Resample/Rolling

pandas/plotting/_core.py

@@ -2172,7 +2172,9 @@ def boxplot(data, column=None, by=None, ax=None, fontsize=None,
         column = 'x'
 
     def _get_colors():
-        return _get_standard_colors(color=kwds.get('color'), num_colors=1)
+        #  num_colors=3 is required as method maybe_color_bp takes the colors
+        #  in positions 0 and 2.
+        return _get_standard_colors(color=kwds.get('color'), num_colors=3)
 
     def maybe_color_bp(bp):
         if 'color' not in kwds:

pandas/plotting/_style.py

@@ -42,6 +42,8 @@ def _get_standard_colors(num_colors=None, colormap=None, color_type='default',
                                                list('bgrcmyk')))
             if isinstance(colors, compat.string_types):
                 colors = list(colors)
+
+            colors = colors[0:num_colors]
         elif color_type == 'random':
             import pandas.core.common as com
 

pandas/tests/plotting/test_misc.py

@@ -215,8 +215,8 @@ def test_parallel_coordinates_with_sorted_labels(self):
 
         df = DataFrame({"feat": [i for i in range(30)],
                         "class": [2 for _ in range(10)] +
-                        [3 for _ in range(10)] +
-                        [1 for _ in range(10)]})
+                                 [3 for _ in range(10)] +
+                                 [1 for _ in range(10)]})
         ax = parallel_coordinates(df, 'class', sort_labels=True)
         polylines, labels = ax.get_legend_handles_labels()
         color_label_tuples = \
@@ -310,6 +310,33 @@ def test_get_standard_colors_random_seed(self):
         color2 = _get_standard_colors(1, color_type='random')
         assert color1 == color2
 
+    def test_get_standard_colors_default_num_colors(self):
+        from pandas.plotting._style import _get_standard_colors
+
+        # Make sure the default color_types returns the specified amount
+        color1 = _get_standard_colors(1, color_type='default')
+        color2 = _get_standard_colors(9, color_type='default')
+        color3 = _get_standard_colors(20, color_type='default')
+        assert len(color1) == 1
+        assert len(color2) == 9
+        assert len(color3) == 20
+
+    def test_plot_single_color(self):
+        # Example from #20585. All 3 bars should have the same color
+        df = DataFrame({'account-start': ['2017-02-03', '2017-03-03',
+                                          '2017-01-01'],
+                        'client': ['Alice Anders', 'Bob Baker',
+                                   'Charlie Chaplin'],
+                        'balance': [-1432.32, 10.43, 30000.00],
+                        'db-id': [1234, 2424, 251],
+                        'proxy-id': [525, 1525, 2542],
+                        'rank': [52, 525, 32],
+                        })
+        ax = df.client.value_counts().plot.bar()
+        colors = lmap(lambda rect: rect.get_facecolor(),
+                      ax.get_children()[0:3])
+        assert all(color == colors[0] for color in colors)
+
     def test_get_standard_colors_no_appending(self):
         # GH20726