ERR: Better error message for missing matplotlib

Closes #19810

Author: TomAugspurger

doc/source/whatsnew/v0.23.0.txt

@@ -958,6 +958,7 @@ Offsets
 
 Numeric
 ^^^^^^^
+- Better error message when matplotlib is not installed (:issue:`19810`).
 - Bug in :meth:`DataFrame.rank` and :meth:`Series.rank` when ``method='dense'`` and ``pct=True`` in which percentile ranks were not being used with the number of distinct observations (:issue:`15630`)
 - Bug in :class:`Series` constructor with an int or float list where specifying ``dtype=str``, ``dtype='str'`` or ``dtype='U'`` failed to convert the data elements to strings (:issue:`16605`)
 - Bug in :class:`Index` multiplication and division methods where operating with a ``Series`` would return an ``Index`` object instead of a ``Series`` object (:issue:`19042`)

pandas/plotting/_core.py

@@ -44,8 +44,9 @@
 try:
     from pandas.plotting import _converter
 except ImportError:
-    pass
+    _HAS_MPL = False
 else:
+    _HAS_MPL = True
     if get_option('plotting.matplotlib.register_converters'):
         _converter.register(explicit=True)
 
@@ -97,6 +98,9 @@ def __init__(self, data, kind=None, by=None, subplots=False, sharex=None,
                  secondary_y=False, colormap=None,
                  table=False, layout=None, **kwds):
 
+        if not _HAS_MPL:
+            raise ImportError("matplotlib is required for plotting.")
+
         _converter._WARN = False
         self.data = data
         self.by = by
@@ -2264,6 +2268,9 @@ def hist_frame(data, column=None, by=None, grid=True, xlabelsize=None,
         ...     }, index= ['pig', 'rabbit', 'duck', 'chicken', 'horse'])
         >>> hist = df.hist(bins=3)
     """
+    if not _HAS_MPL:
+        raise ImportError("matplotlib is required for plotting.")
+
     _converter._WARN = False
     if by is not None:
         axes = grouped_hist(data, column=column, by=by, ax=ax, grid=grid,
@@ -2403,6 +2410,9 @@ def grouped_hist(data, column=None, by=None, ax=None, bins=50, figsize=None,
     -------
     axes: collection of Matplotlib Axes
     """
+    if not _HAS_MPL:
+        raise ImportError("matplotlib is required for plotting.")
+
     _converter._WARN = False
 
     def plot_group(group, ax):
@@ -2469,6 +2479,9 @@ 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)
     """
+    if not _HAS_MPL:
+        raise ImportError("matplotlib is required for plotting.")
+
     _converter._WARN = False
     if subplots is True:
         naxes = len(grouped)

pandas/tests/plotting/test_misc.py

@@ -17,6 +17,14 @@
 from pandas.tests.plotting.common import TestPlotBase, _check_plot_works
 
 
+@td.skip_if_mpl
+def test_import_error_message():
+    df = DataFrame({"A": [1, 2]})
+
+    with tm.assert_raises_regex(ImportError, 'matplotlib is required'):
+        df.plot()
+
+
 @td.skip_if_no_mpl
 class TestSeriesPlots(TestPlotBase):
 

pandas/util/_test_decorators.py

@@ -160,6 +160,8 @@ def decorated_func(func):
 
 skip_if_no_mpl = pytest.mark.skipif(_skip_if_no_mpl(),
                                     reason="Missing matplotlib dependency")
+skip_if_mpl = pytest.mark.skipif(not _skip_if_no_mpl(),
+                                 reason="matplotlib is pressent")
 skip_if_mpl_1_5 = pytest.mark.skipif(_skip_if_mpl_1_5(),
                                      reason="matplotlib 1.5")
 xfail_if_mpl_2_2 = pytest.mark.xfail(_skip_if_mpl_2_2(),