fixup! Remove matplotlib from blacklist

doc/source/whatsnew/v0.21.1.txt

@@ -25,7 +25,7 @@ the converter.
 
 This caused problems for some users, so we're temporarily reverting that change;
 pandas will again register the converters on import. Using the converters
-without explicitly registering the formatters will cause a ``FutureWarning``:
+without explicitly registering the converters will cause a ``FutureWarning``:
 
 .. code-block:: python
 
@@ -42,9 +42,10 @@ without explicitly registering the formatters will cause a ``FutureWarning``:
            >>> from pandas.tseries import converter
            >>> converter.register()
 
-As the error message says, you'll need to register the converts if you intend to
-use them with matplotlib plotting functions. Pandas plotting functions, such as
-``Series.plot``, will register them for you. (:issue:`18301`)
+As the error message says, you'll need to register the converters if you intend
+to use them with matplotlib plotting functions. Pandas plotting functions, such
+as ``Series.plot``, will register them for you calling ``converter.register()``
+first is not necessary. (:issue:`18301`)
 
 .. _whatsnew_0211.enhancements:
 

pandas/plotting/_core.py

@@ -2059,7 +2059,7 @@ def boxplot_frame(self, column=None, by=None, ax=None, fontsize=None, rot=0,
                   grid=True, figsize=None, layout=None,
                   return_type=None, **kwds):
     import matplotlib.pyplot as plt
-    _converter.WARN = False
+    _converter._WARN = False
     ax = boxplot(self, column=column, by=by, ax=ax, fontsize=fontsize,
                  grid=grid, rot=rot, figsize=figsize, layout=layout,
                  return_type=return_type, **kwds)
@@ -2155,7 +2155,7 @@ def hist_frame(data, column=None, by=None, grid=True, xlabelsize=None,
     kwds : other plotting keyword arguments
         To be passed to hist function
     """
-    _converter.WARN = False
+    _converter._WARN = False
     if by is not None:
         axes = grouped_hist(data, column=column, by=by, ax=ax, grid=grid,
                             figsize=figsize, sharex=sharex, sharey=sharey,
@@ -2289,7 +2289,7 @@ def grouped_hist(data, column=None, by=None, ax=None, bins=50, figsize=None,
     -------
     axes: collection of Matplotlib Axes
     """
-    _converter.WARN = False
+    _converter._WARN = False
 
     def plot_group(group, ax):
         ax.hist(group.dropna().values, bins=bins, **kwargs)
@@ -2354,6 +2354,7 @@ def boxplot_frame_groupby(grouped, subplots=True, column=None, fontsize=None,
     >>> grouped = df.unstack(level='lvl1').groupby(level=0, axis=1)
     >>> boxplot_frame_groupby(grouped, subplots=False)
     """
+    _converter._WARN = False
     if subplots is True:
         naxes = len(grouped)
         fig, axes = _subplots(naxes=naxes, squeeze=False,

pandas/tests/plotting/test_converter.py

@@ -45,6 +45,16 @@ def test_registering_no_warning(self):
 
         assert len(w) == 0
 
+    def test_pandas_plots_register(self):
+        pytest.importorskip("matplotlib.pyplot")
+        s = Series(range(12), index=date_range('2017', periods=12))
+        # Set to the "no-warn" state, in case this isn't the first test run
+        converter._WARN = True
+        with tm.assert_produces_warning(None) as w:
+            s.plot()
+
+        assert len(w) == 0
+
 
 class TestDateTimeConverter(object):