Deprecate ._data (#857)

* Deprecate call to dataframe._data

Author: martindurant

fastparquet/dataframe.py

@@ -181,7 +181,7 @@ def set_cats(values, i=i, col=col, **kwargs):
             views[col+'-catdef'] = x
 
     # Patch our blocks with desired-length arrays.  Kids: don't try this at home.
-    mgr = df._data
+    mgr = df._mgr
     for block in mgr.blocks:
         bvalues = block.values
         shape = list(bvalues.shape)
@@ -223,7 +223,7 @@ def set_cats(values, i=i, col=col, **kwargs):
     mgr.axes[-1] = index
 
     # create views
-    for block in df._data.blocks:
+    for block in df._mgr.blocks:
         dtype = block.dtype
         inds = block.mgr_locs.indexer
         if isinstance(inds, slice):

fastparquet/test/test_dataframe.py

@@ -34,7 +34,6 @@ def test_empty():
     assert len(views) == 5
 
 
-@pytest.mark.xfail(reason="df._data is going away")
 def test_empty_tz_utc():
     with warnings.catch_warnings():
         warnings.simplefilter("error")