Fix plotting memory leak and add regression test

Author: qwhelan

doc/source/whatsnew/v0.16.1.txt

@@ -141,7 +141,6 @@ Bug Fixes
 
 
 
-
 - Bug in unequal comparisons between categorical data and a scalar, which was not in the categories (e.g. ``Series(Categorical(list("abc"), ordered=True)) > "d"``. This returned ``False`` for all elements, but now raises a ``TypeError``. Equality comparisons also now return ``False`` for ``==`` and ``True`` for ``!=``. (:issue:`9848`)
 - Bug in DataFrame ``__setitem__`` when right hand side is a dictionary (:issue:`9874`)
 - Bug in ``where`` when dtype is ``datetime64/timedelta64``, but dtype of other is not (:issue:`9804`)
@@ -164,3 +163,4 @@ Bug Fixes
 
 - Fixed latex output for multi-indexed dataframes (:issue:`9778`)
 - Bug causing an exception when setting an empty range using ``DataFrame.loc`` (:issue:`9596`)
+- Fixed memory leak in ``AreaPlot`` and ``LinePlot`` that prevented calls to ``plt.close()`` from having any effect. (:issue:`9003`)

pandas/tests/test_graphics.py

@@ -28,6 +28,8 @@
 from numpy.testing import assert_array_equal, assert_allclose
 from numpy.testing.decorators import slow
 import pandas.tools.plotting as plotting
+import weakref
+import gc
 
 
 def _skip_if_mpl_14_or_dev_boxplot():
@@ -3390,6 +3392,33 @@ def test_sharey_and_ax(self):
                              "y label is invisible but shouldn't")
 
 
+    def test_memory_leak(self):
+        """ Check that every plot type gets properly collected. """
+        import matplotlib.pyplot as plt
+        results = {}
+        for kind in plotting._plot_klass.keys():
+            args = {}
+            if kind in ['hexbin', 'scatter', 'pie']:
+                df = self.hexbin_df
+                args = {'x': 'A', 'y': 'B'}
+            elif kind == 'area':
+                df = self.tdf.abs()
+            else:
+                df = self.tdf
+
+            # Use a weakref so we can see if the object gets collected without
+            # also preventing it from being collected
+            results[kind] = weakref.proxy(df.plot(kind=kind, **args))
+
+        # have matplotlib delete all the figures
+        plt.close('all')
+        # force a garbage collection
+        gc.collect()
+        for key in results:
+            # check that every plot was collected
+            with tm.assertRaises(ReferenceError):
+                # need to actually access something to get an error
+                results[key].lines
 
 @tm.mplskip
 class TestDataFrameGroupByPlots(TestPlotBase):