BUG: Index.copy() honors 'name' parameter (#14302)

closes #14302

Author: Christopher C. Aycock <christopher.aycock@twosigma.com>

Closes #14303 from chrisaycock/master and squashes the following commits:

bbfc79f [Christopher C. Aycock] BUG: Index.copy() honors 'name' parameter (#14302)

Author: Christopher C. Aycock

doc/source/whatsnew/v0.19.0.txt

@@ -1583,3 +1583,4 @@ Bug Fixes
 - Bugs in ``stack``, ``get_dummies``, ``make_axis_dummies`` which don't preserve categorical dtypes in (multi)indexes (:issue:`13854`)
 - ``PeridIndex`` can now accept ``list`` and ``array`` which contains ``pd.NaT`` (:issue:`13430`)
 - Bug in ``df.groupby`` where ``.median()`` returns arbitrary values if grouped dataframe contains empty bins (:issue:`13629`)
+- Bug in ``Index.copy()`` where ``name`` parameter was ignored (:issue:`14302`)

pandas/indexes/base.py

@@ -621,26 +621,40 @@ def _coerce_scalar_to_index(self, item):
 
     @Appender(_index_shared_docs['copy'])
     def copy(self, name=None, deep=False, dtype=None, **kwargs):
-        names = kwargs.get('names')
-        if names is not None and name is not None:
-            raise TypeError("Can only provide one of `names` and `name`")
         if deep:
-            from copy import deepcopy
             new_index = self._shallow_copy(self._data.copy())
-            name = name or deepcopy(self.name)
         else:
             new_index = self._shallow_copy()
-            name = self.name
-        if name is not None:
-            names = [name]
-        if names:
-            new_index = new_index.set_names(names)
+
+        names = kwargs.get('names')
+        names = self._validate_names(name=name, names=names, deep=deep)
+        new_index = new_index.set_names(names)
+
         if dtype:
             new_index = new_index.astype(dtype)
         return new_index
 
     __copy__ = copy
 
+    def _validate_names(self, name=None, names=None, deep=False):
+        """
+        Handles the quirks of having a singular 'name' parameter for general
+        Index and plural 'names' parameter for MultiIndex.
+        """
+        from copy import deepcopy
+        if names is not None and name is not None:
+            raise TypeError("Can only provide one of `names` and `name`")
+        elif names is None and name is None:
+            return deepcopy(self.names) if deep else self.names
+        elif names is not None:
+            if not is_list_like(names):
+                raise TypeError("Must pass list-like as `names`.")
+            return names
+        else:
+            if not is_list_like(name):
+                return [name]
+            return name
+
     def __unicode__(self):
         """
         Return a string representation for this object.

pandas/indexes/multi.py

@@ -346,7 +346,7 @@ def set_labels(self, labels, level=None, inplace=False,
     labels = property(fget=_get_labels, fset=__set_labels)
 
     def copy(self, names=None, dtype=None, levels=None, labels=None,
-             deep=False, _set_identity=False):
+             deep=False, _set_identity=False, **kwargs):
         """
         Make a copy of this object. Names, dtype, levels and labels can be
         passed and will be set on new copy.
@@ -368,15 +368,20 @@ def copy(self, names=None, dtype=None, levels=None, labels=None,
         ``deep``, but if ``deep`` is passed it will attempt to deepcopy.
         This could be potentially expensive on large MultiIndex objects.
         """
+        name = kwargs.get('name')
+        names = self._validate_names(name=name, names=names, deep=deep)
+
         if deep:
             from copy import deepcopy
-            levels = levels if levels is not None else deepcopy(self.levels)
-            labels = labels if labels is not None else deepcopy(self.labels)
-            names = names if names is not None else deepcopy(self.names)
+            if levels is None:
+                levels = deepcopy(self.levels)
+            if labels is None:
+                labels = deepcopy(self.labels)
         else:
-            levels = self.levels
-            labels = self.labels
-            names = self.names
+            if levels is None:
+                levels = self.levels
+            if labels is None:
+                labels = self.labels
         return MultiIndex(levels=levels, labels=labels, names=names,
                           sortorder=self.sortorder, verify_integrity=False,
                           _set_identity=_set_identity)

pandas/tests/indexes/test_base.py

@@ -1817,6 +1817,30 @@ def test_copy_name(self):
             s3 = s1 * s2
         self.assertEqual(s3.index.name, 'mario')
 
+    def test_copy_name2(self):
+        # Check that adding a "name" parameter to the copy is honored
+        # GH14302
+        idx = pd.Index([1, 2], name='MyName')
+        idx1 = idx.copy()
+
+        self.assertTrue(idx.equals(idx1))
+        self.assertEqual(idx.name, 'MyName')
+        self.assertEqual(idx1.name, 'MyName')
+
+        idx2 = idx.copy(name='NewName')
+
+        self.assertTrue(idx.equals(idx2))
+        self.assertEqual(idx.name, 'MyName')
+        self.assertEqual(idx2.name, 'NewName')
+
+        idx3 = idx.copy(names=['NewName'])
+
+        self.assertTrue(idx.equals(idx3))
+        self.assertEqual(idx.name, 'MyName')
+        self.assertEqual(idx.names, ['MyName'])
+        self.assertEqual(idx3.name, 'NewName')
+        self.assertEqual(idx3.names, ['NewName'])
+
     def test_union_base(self):
         idx = self.create_index()
         first = idx[3:]

pandas/tests/indexes/test_multi.py

@@ -415,6 +415,28 @@ def test_set_value_keeps_names(self):
         self.assertIsNone(df.is_copy)
         self.assertEqual(df.index.names, ('Name', 'Number'))
 
+    def test_copy_names(self):
+        # Check that adding a "names" parameter to the copy is honored
+        # GH14302
+        multi_idx = pd.Index([(1, 2), (3, 4)], names=['MyName1', 'MyName2'])
+        multi_idx1 = multi_idx.copy()
+
+        self.assertTrue(multi_idx.equals(multi_idx1))
+        self.assertEqual(multi_idx.names, ['MyName1', 'MyName2'])
+        self.assertEqual(multi_idx1.names, ['MyName1', 'MyName2'])
+
+        multi_idx2 = multi_idx.copy(names=['NewName1', 'NewName2'])
+
+        self.assertTrue(multi_idx.equals(multi_idx2))
+        self.assertEqual(multi_idx.names, ['MyName1', 'MyName2'])
+        self.assertEqual(multi_idx2.names, ['NewName1', 'NewName2'])
+
+        multi_idx3 = multi_idx.copy(name=['NewName1', 'NewName2'])
+
+        self.assertTrue(multi_idx.equals(multi_idx3))
+        self.assertEqual(multi_idx.names, ['MyName1', 'MyName2'])
+        self.assertEqual(multi_idx3.names, ['NewName1', 'NewName2'])
+
     def test_names(self):
 
         # names are assigned in __init__