DEPR: change Panel DeprecationWarning -> FutureWarning

closes pandas-dev#18324

Author: jreback

doc/source/whatsnew/v0.23.0.txt

@@ -288,6 +288,8 @@ Deprecations
 - ``Series.valid`` is deprecated. Use :meth:`Series.dropna` instead (:issue:`18800`).
 - :func:`read_excel` has deprecated the ``skip_footer`` parameter. Use ``skipfooter`` instead (:issue:`18836`)
 - The ``is_copy`` attribute is deprecated and will be removed in a future version (:issue:`18801`).
+- ``Panel`` is now a ``FutureWarning``, previsouly a ``DeprecationWarning`` and will be removed in a future version (:issue:`18324`)
+
 
 .. _whatsnew_0230.prior_deprecations:
 

pandas/core/panel.py

@@ -151,7 +151,7 @@ def __init__(self, data=None, items=None, major_axis=None, minor_axis=None,
                       "http://xarray.pydata.org/en/stable/.\n"
                       "Pandas provides a `.to_xarray()` method to help "
                       "automate this conversion.\n",
-                      DeprecationWarning, stacklevel=3)
+                      FutureWarning, stacklevel=3)
 
         self._init_data(data=data, items=items, major_axis=major_axis,
                         minor_axis=minor_axis, copy=copy, dtype=dtype)

pandas/tests/generic/test_label_or_level_utils.py

@@ -46,7 +46,7 @@ def df_duplabels(df):
 
 @pytest.fixture
 def panel():
-    with tm.assert_produces_warning(DeprecationWarning,
+    with tm.assert_produces_warning(FutureWarning,
                                     check_stacklevel=False):
         return pd.Panel()