BUG: repair 'style' kwd handling in DataFrame.plot (#21003)

doc/source/whatsnew/v1.1.0.rst

@@ -703,11 +703,12 @@ I/O
 Plotting
 ^^^^^^^^
 
-- :func:`.plot` for line/bar now accepts color by dictonary (:issue:`8193`).
+- :func:`.plot` for line/bar now accepts color by dictionary (:issue:`8193`).
 - Bug in :meth:`DataFrame.plot.hist` where weights are not working for multiple columns (:issue:`33173`)
 - Bug in :meth:`DataFrame.boxplot` and :meth:`DataFrame.plot.boxplot` lost color attributes of ``medianprops``, ``whiskerprops``, ``capprops`` and ``medianprops`` (:issue:`30346`)
 - Bug in :meth:`DataFrame.hist` where the order of ``column`` argument was ignored (:issue:`29235`)
 - Bug in :meth:`DataFrame.plot.scatter` that when adding multiple plots with different ``cmap``, colorbars alway use the first ``cmap`` (:issue:`33389`)
+- Bug in :meth:`DataFrame.plot` where a marker letter in the ``style`` keyword sometimes causes a ``ValueError`` (:issue:`21003`)
 
 
 Groupby/resample/rolling

pandas/plotting/_matplotlib/core.py

@@ -1,4 +1,3 @@
-import re
 from typing import Optional
 import warnings
 
@@ -40,6 +39,15 @@
 )
 
 
+def _color_in_style(style: str) -> bool:
+    """
+    Check if there is a color letter in the style string.
+    """
+    from matplotlib.colors import BASE_COLORS
+
+    return not set(BASE_COLORS).isdisjoint(style)
+
+
 class MPLPlot:
     """
     Base class for assembling a pandas plot using matplotlib
@@ -193,7 +201,6 @@ def __init__(
         self._validate_color_args()
 
     def _validate_color_args(self):
-        import matplotlib.colors
 
         if (
             "color" in self.kwds
@@ -226,13 +233,12 @@ def _validate_color_args(self):
                 styles = [self.style]
             # need only a single match
             for s in styles:
-                for char in s:
-                    if char in matplotlib.colors.BASE_COLORS:
-                        raise ValueError(
-                            "Cannot pass 'style' string with a color symbol and "
-                            "'color' keyword argument. Please use one or the other or "
-                            "pass 'style' without a color symbol"
-                        )
+                if _color_in_style(s):
+                    raise ValueError(
+                        "Cannot pass 'style' string with a color symbol and "
+                        "'color' keyword argument. Please use one or the "
+                        "other or pass 'style' without a color symbol"
+                    )
 
     def _iter_data(self, data=None, keep_index=False, fillna=None):
         if data is None:
@@ -723,7 +729,7 @@ def _apply_style_colors(self, colors, kwds, col_num, label):
                 style = self.style
 
         has_color = "color" in kwds or self.colormap is not None
-        nocolor_style = style is None or re.match("[a-z]+", style) is None
+        nocolor_style = style is None or not _color_in_style(style)
         if (has_color or self.subplots) and nocolor_style:
             if isinstance(colors, dict):
                 kwds["color"] = colors[label]

pandas/tests/plotting/test_frame.py

@@ -204,6 +204,23 @@ def test_color_and_style_arguments(self):
         with pytest.raises(ValueError):
             df.plot(color=["red", "black"], style=["k-", "r--"])
 
+    def test_color_and_marker(self):
+        # GH21003 - code sample from 2018-05-10 is equivalent to this test
+        df = DataFrame(np.random.random((7, 4)))
+        # combining a color string and a marker letter should be allowed
+        df.plot(color="green", style="d")  # d for diamond
+
+    def test_color_list_and_marker(self):
+        # GH21003 - code sample from 2020-04-23 is equivalent to this test
+        df = DataFrame(np.random.random((7, 4)))
+        color_list = ["yellow", "red", "green", "blue"]
+        ax = df.plot(color=color_list, style="d")
+        # Before this patch was introduced, the previous line of code resulted
+        # in a plot where each individual line was assigned a list of colors:
+        # ax.lines[i].get_color() == ['yellow', 'red', 'green', 'blue']
+        # which resulted in a ValueError when plt.draw() was called.
+        assert [line.get_color() for line in ax.lines] == color_list
+
     def test_nonnumeric_exclude(self):
         df = DataFrame({"A": ["x", "y", "z"], "B": [1, 2, 3]})
         ax = df.plot()

pandas/tests/plotting/test_series.py

@@ -933,4 +933,4 @@ def test_plot_no_numeric_data(self):
     def test_style_single_ok(self):
         s = pd.Series([1, 2])
         ax = s.plot(style="s", color="C3")
-        assert ax.lines[0].get_color() == ["C3"]
+        assert ax.lines[0].get_color() == "C3"