Empty series now has the dtype object instead of float64

Author: SaturnFromTitan

pandas/core/series.py

@@ -319,8 +319,13 @@ def __init__(
                 elif copy:
                     data = data.copy()
             else:
-                data = sanitize_array(data, index, dtype, copy, raise_cast_failure=True)
+                if isinstance(data, (list, tuple)) and not data and dtype is None:
+                    # makes sure that empty Series has dtype object
+                    # while this inconsistent with numpy, it is consistent
+                    # with the behaviour of DataFrame and Index
+                    dtype = np.dtype(object)
 
+                data = sanitize_array(data, index, dtype, copy, raise_cast_failure=True)
                 data = SingleBlockManager(data, index, fastpath=True)
 
         generic.NDFrame.__init__(self, data, fastpath=True)

pandas/tests/series/test_apply.py

@@ -513,7 +513,7 @@ def test_map_empty(self, index):
         s = Series(index)
         result = s.map({})
 
-        expected = pd.Series(np.nan, index=s.index)
+        expected = pd.Series(np.nan, index=s.index, dtype="object")
         tm.assert_series_equal(result, expected)
 
     def test_map_compat(self):

pandas/tests/series/test_constructors.py

@@ -58,6 +58,9 @@ def test_empty_constructor(self, constructor, check_index_type):
         assert len(result.index) == 0
         tm.assert_series_equal(result, expected, check_index_type=check_index_type)
 
+    def test_dtype_of_empty_series(self):
+        assert Series().dtype == object
+
     def test_invalid_dtype(self):
         # GH15520
         msg = "not understood"

pandas/tests/series/test_operators.py

@@ -761,7 +761,7 @@ def test_ops_datetimelike_align(self):
         tm.assert_series_equal(result, expected)
 
     def test_operators_corner(self, datetime_series):
-        empty = Series([], index=Index([]))
+        empty = Series([], index=Index([]), dtype="float64")
 
         result = datetime_series + empty
         assert np.isnan(result).all()

pandas/tests/series/test_quantile.py

@@ -67,7 +67,7 @@ def test_quantile_multi(self, datetime_series):
 
         result = datetime_series.quantile([])
         expected = pd.Series(
-            [], name=datetime_series.name, index=Index([], dtype=float)
+            [], name=datetime_series.name, index=Index([], dtype=float), dtype="float64"
         )
         tm.assert_series_equal(result, expected)