Avoid checking against types in is_dataframe_like (dask#4418)

dask/dataframe/tests/test_dataframe.py

@@ -553,6 +553,12 @@ def test_map_partitions():
     assert result.dtype == np.float64 and result.compute() == 4.0
 
 
+def test_map_partitions_type():
+    result = d.map_partitions(type).compute(scheduler='single-threaded')
+    assert isinstance(result, pd.Series)
+    assert all(x == pd.DataFrame for x in result)
+
+
 def test_map_partitions_names():
     func = lambda x: x
     assert (sorted(dd.map_partitions(func, d, meta=d).dask) ==

dask/dataframe/tests/test_utils_dataframe.py

@@ -337,14 +337,17 @@ def test_is_dataframe_like():
     assert is_dataframe_like(df)
     assert not is_dataframe_like(df.x)
     assert not is_dataframe_like(df.index)
+    assert not is_dataframe_like(pd.DataFrame)
 
     assert not is_series_like(df)
     assert is_series_like(df.x)
     assert not is_series_like(df.index)
+    assert not is_series_like(pd.Series)
 
     assert not is_index_like(df)
     assert not is_index_like(df.x)
     assert is_index_like(df.index)
+    assert not is_index_like(pd.Index)
 
     ddf = dd.from_pandas(df, npartitions=1)
     assert is_dataframe_like(ddf)

dask/dataframe/utils.py

@@ -497,18 +497,18 @@ def _nonempty_series(s, idx=None):
 
 def is_dataframe_like(df):
     """ Looks like a Pandas DataFrame """
-    return set(dir(df)) > {'dtypes', 'columns', 'groupby', 'head'}
+    return set(dir(df)) > {'dtypes', 'columns', 'groupby', 'head'} and not isinstance(df, type)
 
 
 def is_series_like(s):
     """ Looks like a Pandas Series """
-    return set(dir(s)) > {'name', 'dtype', 'groupby', 'head'}
+    return set(dir(s)) > {'name', 'dtype', 'groupby', 'head'} and not isinstance(s, type)
 
 
 def is_index_like(s):
     """ Looks like a Pandas Index """
     attrs = set(dir(s))
-    return attrs > {'name', 'dtype'} and 'head' not in attrs
+    return attrs > {'name', 'dtype'} and 'head' not in attrs and not isinstance(s, type)
 
 
 def check_meta(x, meta, funcname=None, numeric_equal=True):