From 531b9e5afa8efa8252daf3d361b0a21a9ec7fd11 Mon Sep 17 00:00:00 2001
From: Morgan Stuart <morgansstuart243@gmail.com>
Date: Sat, 15 Jul 2017 13:59:41 -0400
Subject: [PATCH] Fix for Issue #12565 - font size on secondary_y

There may be other plotting methods that need testing.
---
 doc/source/whatsnew/v0.21.0.txt     |  2 +-
 pandas/plotting/_core.py            |  9 +++++++++
 pandas/tests/plotting/test_frame.py | 16 ++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v0.21.0.txt b/doc/source/whatsnew/v0.21.0.txt
index bd19d71182762..483ce2232976f 100644
--- a/doc/source/whatsnew/v0.21.0.txt
+++ b/doc/source/whatsnew/v0.21.0.txt
@@ -166,7 +166,7 @@ I/O
 
 Plotting
 ^^^^^^^^
-
+- Bug in plotting methods using ``secondary_y`` and ``fontsize`` not setting secondary axes font size (:issue:`12565`)
 
 
 Groupby/Resample/Rolling
diff --git a/pandas/plotting/_core.py b/pandas/plotting/_core.py
index f8e83aea03594..0fa2b6b79da75 100644
--- a/pandas/plotting/_core.py
+++ b/pandas/plotting/_core.py
@@ -379,6 +379,11 @@ def _post_plot_logic_common(self, ax, data):
             self._apply_axis_properties(ax.xaxis, rot=self.rot,
                                         fontsize=self.fontsize)
             self._apply_axis_properties(ax.yaxis, fontsize=self.fontsize)
+
+            if hasattr(ax, 'right_ax'):
+                self._apply_axis_properties(ax.right_ax.yaxis,
+                                            fontsize=self.fontsize)
+
         elif self.orientation == 'horizontal':
             if self._need_to_set_index:
                 yticklabels = [labels.get(y, '') for y in ax.get_yticks()]
@@ -386,6 +391,10 @@ def _post_plot_logic_common(self, ax, data):
             self._apply_axis_properties(ax.yaxis, rot=self.rot,
                                         fontsize=self.fontsize)
             self._apply_axis_properties(ax.xaxis, fontsize=self.fontsize)
+
+            if hasattr(ax, 'right_ax'):
+                self._apply_axis_properties(ax.right_ax.yaxis,
+                                            fontsize=self.fontsize)
         else:  # pragma no cover
             raise ValueError
 
diff --git a/pandas/tests/plotting/test_frame.py b/pandas/tests/plotting/test_frame.py
index 7878740f64e55..22307b37ffd36 100644
--- a/pandas/tests/plotting/test_frame.py
+++ b/pandas/tests/plotting/test_frame.py
@@ -2733,6 +2733,22 @@ def test_rcParams_bar_colors(self):
                 barplot = pd.DataFrame([[1, 2, 3]]).plot(kind="bar")
         assert color_tuples == [c.get_facecolor() for c in barplot.patches]
 
+    @pytest.mark.parametrize('method', ['line', 'barh', 'bar'])
+    def test_secondary_axis_font_size(self, method):
+        df = (pd.DataFrame(np.random.randn(15, 2),
+                           columns=list('AB'))
+              .assign(C=lambda df: df.B.cumsum())
+              .assign(D=lambda df: df.C*1.1))
+
+        fontsize = 20
+        sy = ['C', 'D']
+
+        kwargs = dict(secondary_y=sy, fontsize=fontsize,
+                      mark_right=True)
+        ax = getattr(df.plot, method)(**kwargs)
+        self._check_ticks_props(axes=ax.right_ax,
+                                ylabelsize=fontsize)
+
 
 def _generate_4_axes_via_gridspec():
     import matplotlib.pyplot as plt