remove extra legend handles

Author: MarcoGorelli

doc/source/whatsnew/v1.3.0.rst

@@ -694,7 +694,9 @@ Plotting
 
 - Bug in :func:`scatter_matrix` raising when 2d ``ax`` argument passed (:issue:`16253`)
 - Prevent warnings when matplotlib's ``constrained_layout`` is enabled (:issue:`25261`)
--
+- Bug in :func:`DataFrame.plot` was showing the wrong colors in the legend if the function was called repeatedly and some calls used ``yerr`` while others didn't (:issue:`39522`)
+- Bug in :func:`DataFrame.plot` was showing the wrong colors in the legend if the function was called repeatedly and some calls used ``secondary_y`` and others use ``legend=False`` (:issue:`40044`)
+
 
 Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^

pandas/plotting/_matplotlib/core.py

@@ -599,7 +599,7 @@ def _append_legend_handles_labels(self, handle: Artist, label: str) -> None:
         self.legend_labels.append(label)
 
     def _make_legend(self):
-        ax, leg, handle = self._get_ax_legend_handle(self.axes[0])
+        ax, leg = self._get_ax_legend(self.axes[0])
 
         handles = []
         labels = []
@@ -609,7 +609,7 @@ def _make_legend(self):
             if leg is not None:
                 title = leg.get_title().get_text()
                 # Replace leg.LegendHandles because it misses marker info
-                handles.extend(handle)
+                handles = leg.legendHandles
                 labels = [x.get_text() for x in leg.get_texts()]
 
             if self.legend:
@@ -640,22 +640,20 @@ def _make_legend(self):
                 if ax.get_visible():
                     ax.legend(loc="best")
 
-    def _get_ax_legend_handle(self, ax: Axes):
+    def _get_ax_legend(self, ax: Axes):
         """
-        Take in axes and return ax, legend and handle under different scenarios
+        Take in axes and return ax and legend under different scenarios
         """
         leg = ax.get_legend()
 
-        # Get handle from axes
-        handle, _ = ax.get_legend_handles_labels()
         other_ax = getattr(ax, "left_ax", None) or getattr(ax, "right_ax", None)
         other_leg = None
         if other_ax is not None:
             other_leg = other_ax.get_legend()
         if leg is None and other_leg is not None:
             leg = other_leg
             ax = other_ax
-        return ax, leg, handle
+        return ax, leg
 
     @cache_readonly
     def plt(self):

pandas/tests/plotting/frame/test_frame_legend.py

@@ -0,0 +1,31 @@
+from matplotlib.collections import LineCollection
+from matplotlib.lines import Line2D
+
+from pandas import DataFrame
+
+
+def test_mixed_yerr():
+    # https://github.com/pandas-dev/pandas/issues/39522
+    df = DataFrame([{"x": 1, "a": 1, "b": 1}, {"x": 2, "a": 2, "b": 3}])
+
+    ax = df.plot("x", "a", c="orange", yerr=0.1, label="orange")
+    df.plot("x", "b", c="blue", yerr=None, ax=ax, label="blue")
+
+    legend = ax.get_legend()
+    result_handles = legend.legendHandles
+
+    assert isinstance(result_handles[0], LineCollection)
+    assert isinstance(result_handles[1], Line2D)
+
+
+def test_legend_false():
+    # https://github.com/pandas-dev/pandas/issues/40044
+    df = DataFrame({"a": [1, 1], "b": [2, 3]})
+    df2 = DataFrame({"d": [2.5, 2.5]})
+
+    ax = df.plot(legend=True, color={"a": "blue", "b": "green"}, secondary_y="b")
+    df2.plot(legend=True, color={"d": "red"}, ax=ax)
+    legend = ax.get_legend()
+    result = [handle.get_color() for handle in legend.legendHandles]
+    expected = ["blue", "green", "red"]
+    assert result == expected