TST/CLN: empty DataFrames and some 'empty' Series (#25690)

Author: simonjayhawkins

pandas/tests/frame/test_arithmetic.py

@@ -435,7 +435,7 @@ def test_arith_flex_zero_len_raises(self):
         # GH 19522 passing fill_value to frame flex arith methods should
         # raise even in the zero-length special cases
         ser_len0 = pd.Series([])
-        df_len0 = pd.DataFrame([], columns=['A', 'B'])
+        df_len0 = pd.DataFrame(columns=['A', 'B'])
         df = pd.DataFrame([[1, 2], [3, 4]], columns=['A', 'B'])
 
         with pytest.raises(NotImplementedError, match='fill_value'):

pandas/tests/frame/test_combine_concat.py

@@ -170,8 +170,8 @@ def test_append_list_of_series_dicts(self):
     def test_append_empty_dataframe(self):
 
         # Empty df append empty df
-        df1 = DataFrame([])
-        df2 = DataFrame([])
+        df1 = DataFrame()
+        df2 = DataFrame()
         result = df1.append(df2)
         expected = df1.copy()
         assert_frame_equal(result, expected)
@@ -581,18 +581,18 @@ def test_combine_first(self, float_frame):
         assert_series_equal(combined['A'].reindex(g.index), g['A'])
 
         # corner cases
-        comb = float_frame.combine_first(DataFrame({}))
+        comb = float_frame.combine_first(DataFrame())
         assert_frame_equal(comb, float_frame)
 
-        comb = DataFrame({}).combine_first(float_frame)
+        comb = DataFrame().combine_first(float_frame)
         assert_frame_equal(comb, float_frame)
 
         comb = float_frame.combine_first(DataFrame(index=["faz", "boo"]))
         assert "faz" in comb.index
 
         # #2525
         df = DataFrame({'a': [1]}, index=[datetime(2012, 1, 1)])
-        df2 = DataFrame({}, columns=['b'])
+        df2 = DataFrame(columns=['b'])
         result = df.combine_first(df2)
         assert 'b' in result
 

pandas/tests/frame/test_constructors.py

@@ -16,8 +16,8 @@
 
 import pandas as pd
 from pandas import (
-    Categorical, DataFrame, Index, MultiIndex, Series, Timedelta, Timestamp,
-    compat, date_range, isna)
+    Categorical, DataFrame, Index, MultiIndex, RangeIndex, Series, Timedelta,
+    Timestamp, compat, date_range, isna)
 from pandas.tests.frame.common import TestData
 import pandas.util.testing as tm
 
@@ -28,12 +28,36 @@
 
 class TestDataFrameConstructors(TestData):
 
-    def test_constructor(self):
-        df = DataFrame()
-        assert len(df.index) == 0
+    @pytest.mark.parametrize('constructor', [
+        lambda: DataFrame(),
+        lambda: DataFrame(None),
+        lambda: DataFrame({}),
+        lambda: DataFrame(()),
+        lambda: DataFrame([]),
+        lambda: DataFrame((x for x in [])),
+        lambda: DataFrame(data=None),
+        lambda: DataFrame(data={}),
+        lambda: DataFrame(data=()),
+        lambda: DataFrame(data=[]),
+        lambda: DataFrame(data=(x for x in []))
+    ])
+    def test_empty_constructor(self, constructor):
+        expected = DataFrame()
+        result = constructor()
+        assert len(result.index) == 0
+        assert len(result.columns) == 0
+        tm.assert_frame_equal(result, expected)
 
-        df = DataFrame(data={})
-        assert len(df.index) == 0
+    @pytest.mark.parametrize('emptylike,expected_index,expected_columns', [
+        ([[]], RangeIndex(1), RangeIndex(0)),
+        ([[], []], RangeIndex(2), RangeIndex(0)),
+        ([(x for x in [])], RangeIndex(1), RangeIndex(0))
+    ])
+    def test_emptylike_constructor(
+            self, emptylike, expected_index, expected_columns):
+        expected = DataFrame(index=expected_index, columns=expected_columns)
+        result = DataFrame(emptylike)
+        tm.assert_frame_equal(result, expected)
 
     def test_constructor_mixed(self):
         index, data = tm.getMixedTypeDict()
@@ -91,7 +115,7 @@ def test_constructor_dtype_list_data(self):
 
     def test_constructor_list_frames(self):
         # see gh-3243
-        result = DataFrame([DataFrame([])])
+        result = DataFrame([DataFrame()])
         assert result.shape == (1, 0)
 
         result = DataFrame([DataFrame(dict(A=lrange(5)))])
@@ -258,7 +282,7 @@ def test_constructor_dict(self):
         frame = DataFrame({}, index=idx)
         assert frame.index is idx
 
-        # empty with index and columns
+        # empty dict with index and columns
         idx = Index([0, 1, 2])
         frame = DataFrame({}, index=idx, columns=idx)
         assert frame.index is idx
@@ -1105,7 +1129,7 @@ def test_constructor_list_of_series(self):
         result2 = DataFrame(data, index=np.arange(6))
         tm.assert_frame_equal(result, result2)
 
-        result = DataFrame([Series({})])
+        result = DataFrame([Series()])
         expected = DataFrame(index=[0])
         tm.assert_frame_equal(result, expected)
 

pandas/tests/frame/test_reshape.py

@@ -52,7 +52,7 @@ def test_pivot_duplicates(self):
             data.pivot('a', 'b', 'c')
 
     def test_pivot_empty(self):
-        df = DataFrame({}, columns=['a', 'b', 'c'])
+        df = DataFrame(columns=['a', 'b', 'c'])
         result = df.pivot('a', 'b', 'c')
         expected = DataFrame()
         tm.assert_frame_equal(result, expected, check_names=False)

pandas/tests/groupby/test_function.py

@@ -1064,8 +1064,8 @@ def test_size(df):
         tm.assert_series_equal(left, right, check_names=False)
 
     # GH11699
-    df = DataFrame([], columns=['A', 'B'])
-    out = Series([], dtype='int64', index=Index([], name='A'))
+    df = DataFrame(columns=['A', 'B'])
+    out = Series(dtype='int64', index=Index([], name='A'))
     tm.assert_series_equal(df.groupby('A').size(), out)
 
 

pandas/tests/groupby/test_groupby.py

@@ -296,7 +296,7 @@ def f1(x):
         if y.empty:
             multiindex = MultiIndex(levels=[[]] * 2, codes=[[]] * 2,
                                     names=['b', 'c'])
-            res = DataFrame(None, columns=['a'], index=multiindex)
+            res = DataFrame(columns=['a'], index=multiindex)
             return res
         else:
             y = y.set_index(['b', 'c'])
@@ -315,7 +315,7 @@ def f3(x):
         if y.empty:
             multiindex = MultiIndex(levels=[[]] * 2, codes=[[]] * 2,
                                     names=['foo', 'bar'])
-            res = DataFrame(None, columns=['a', 'b'], index=multiindex)
+            res = DataFrame(columns=['a', 'b'], index=multiindex)
             return res
         else:
             return y

pandas/tests/groupby/test_grouping.py

@@ -643,7 +643,7 @@ def test_groupby_with_single_column(self):
         df = pd.DataFrame({'a': list('abssbab')})
         tm.assert_frame_equal(df.groupby('a').get_group('a'), df.iloc[[0, 5]])
         # GH 13530
-        exp = pd.DataFrame([], index=pd.Index(['a', 'b', 's'], name='a'))
+        exp = pd.DataFrame(index=pd.Index(['a', 'b', 's'], name='a'))
         tm.assert_frame_equal(df.groupby('a').count(), exp)
         tm.assert_frame_equal(df.groupby('a').sum(), exp)
         tm.assert_frame_equal(df.groupby('a').nth(1), exp)

pandas/tests/indexing/common.py

@@ -85,8 +85,8 @@ def setup_method(self, method):
         self.frame_ts_rev = DataFrame(np.random.randn(4, 4),
                                       index=dates_rev)
 
-        self.frame_empty = DataFrame({})
-        self.series_empty = Series({})
+        self.frame_empty = DataFrame()
+        self.series_empty = Series()
 
         # form agglomerates
         for o in self._objs:

pandas/tests/io/json/test_json_table_schema.py

@@ -459,7 +459,7 @@ def test_set_names_unset(self, idx, nm, prop):
     ])
     def test_warns_non_roundtrippable_names(self, idx):
         # GH 19130
-        df = pd.DataFrame([[]], index=idx)
+        df = pd.DataFrame(index=idx)
         df.index.name = 'index'
         with tm.assert_produces_warning():
             set_default_names(df)
@@ -566,7 +566,7 @@ def test_multiindex(self, index_names):
 
     def test_empty_frame_roundtrip(self):
         # GH 21287
-        df = pd.DataFrame([], columns=['a', 'b', 'c'])
+        df = pd.DataFrame(columns=['a', 'b', 'c'])
         expected = df.copy()
         out = df.to_json(orient='table')
         result = pd.read_json(out, orient='table')

pandas/tests/io/json/test_pandas.py

@@ -54,7 +54,7 @@ def setup(self, datapath):
         self.objSeries.name = 'objects'
 
         self.empty_series = Series([], index=[])
-        self.empty_frame = DataFrame({})
+        self.empty_frame = DataFrame()
 
         self.frame = _frame.copy()
         self.frame2 = _frame2.copy()