Move warning into _union method

Author: reidy-p

Diff for: pandas/bin/activate

@@ -0,0 +1 @@
+/Users/paul/anaconda/bin/activate

Diff for: pandas/bin/conda

@@ -0,0 +1 @@
+/Users/paul/anaconda/bin/conda

Diff for: pandas/bin/deactivate

@@ -0,0 +1 @@
+/Users/paul/anaconda/bin/deactivate

Diff for: pandas/core/indexes/base.py

@@ -2301,6 +2301,7 @@ def _union_incompatible_dtypes(self, other, sort):
         -------
         Index
         """
+
         this = self.astype(object, copy=False)
         # cast to Index for when `other` is list-like
         other = Index(other).astype(object, copy=False)
@@ -2415,6 +2416,11 @@ def _union(self, other, sort):
         Index
         """
 
+        if sort is None:
+            warnings.warn("sort='None' is deprecated, and will be "
+                          "removed in a future version.",
+                          FutureWarning, stacklevel=3)
+
         if not len(other) or self.equals(other):
             res = self._get_reconciled_name_object(other)
             if sort:

Diff for: pandas/tests/indexes/test_base.py

@@ -799,7 +799,7 @@ def test_chained_union(self, sort):
         j1 = Index([1, 2], name='j1')
         j2 = Index([], name='j2')
         j3 = Index([], name='j3')
-        with tm.assert_produces_warning(warning):
+        with tm.assert_produces_warning(warning, check_stacklevel=False):
             union = j1.union(j2.union(j3, sort=sort), sort=sort)
             expected = j1.union(j2, sort=sort).union(j3, sort=sort)
         tm.assert_index_equal(union, expected)
@@ -874,7 +874,7 @@ def test_union_from_iterables(self, klass, sort):
         case = klass(second.values)
 
         warning = FutureWarning if sort is None else None
-        with tm.assert_produces_warning(warning):
+        with tm.assert_produces_warning(warning, check_stacklevel=False):
             result = first.union(case, sort=sort)
 
         if sort is not False:
@@ -895,8 +895,7 @@ def test_union_identity(self, sort):
 
         # This should no longer be the same object, since [] is not consistent,
         # both objects will be recast to dtype('O')
-        union = first.union([], sort=sort)
-        with tm.assert_produces_warning(warning):
+        with tm.assert_produces_warning(warning, check_stacklevel=False):
             union = first.union([], sort=sort)
         assert (union is first) is (not sort)
 
@@ -2263,7 +2262,7 @@ def test_union_different_type_base(self, klass):
         first = index[3:]
         second = index[:5]
 
-        with tm.assert_produces_warning(FutureWarning):
+        with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
             result = first.union(klass(second.values))
 
         assert tm.equalContents(result, index)