Address jreback comments

Author: Dr-Irv

doc/source/whatsnew/v0.20.0.txt

@@ -185,12 +185,12 @@ Other enhancements
 - ``Series/DataFrame.asfreq()`` have gained a ``fill_value`` parameter, to fill missing values (:issue:`3715`).
 - ``Series/DataFrame.resample.asfreq`` have gained a ``fill_value`` parameter, to fill missing values during resampling (:issue:`3715`).
 - ``pandas.tools.hashing`` has gained a ``hash_tuples`` routine, and ``hash_pandas_object`` has gained the ability to hash a ``MultiIndex`` (:issue:`15224`)
-- ``Series/DataFrame.squeeze()`` have gained the ``axis`` parameter. (:issue:`15339`)<<<<<<< f4edb053e17e51e8c2bed7c16755c4f7f3222117
+- ``Series/DataFrame.squeeze()`` have gained the ``axis`` parameter. (:issue:`15339`)
 - ``DataFrame.to_excel()`` has a new ``freeze_panes`` parameter to turn on Freeze Panes when exporting to Excel (:issue:`15160`)
 - HTML table output skips ``colspan`` or ``rowspan`` attribute if equal to 1. (:issue:`15403`)
 - ``pd.TimedeltaIndex`` now has a custom datetick formatter specifically designed for nanosecond level precision (:issue:`8711`)
 - ``pd.types.concat.union_categoricals`` gained the ``ignore_ordered`` argument to allow ignoring the ordered attribute of unioned categoricals (:issue:`13410`). See the :ref:`categorical union docs <categorical.union>` for more information.
-- Using numerical names in ``MultiIndex`` causes less errors. (:issue:`12223`) (:issue:`15262`)
+- Fixed issue when using ``pd.concat`` that affected ``MultiIndex`` output formatting when names of index were int (:issue:`12223`, :issue:`15262`)
 
 .. _ISO 8601 duration: https://en.wikipedia.org/wiki/ISO_8601#Durations
 

pandas/indexes/base.py

@@ -2353,8 +2353,21 @@ def get_level_values(self, level):
         return self
 
     def _get_level_values(self, num):
-        # Used to mirror implementation for MultiIndex
-        # GH #10461
+        """
+        Return vector of label values for requested level, equal to the length
+        of the index
+
+        **this is an internal method**
+
+        Parameters
+        ----------
+        level : int
+
+        Returns
+        -------
+        values : ndarray
+        """
+        # Needed to address discussion in GH #10461
         return self.get_level_values(num)
 
     _index_shared_docs['get_indexer'] = """

pandas/indexes/multi.py

@@ -684,7 +684,7 @@ def is_monotonic_increasing(self):
         """
 
         # reversed() because lexsort() wants the most significant key last.
-        values = [self._get_level_values(i)
+        values = [self._get_level_values(i).values
                   for i in reversed(range(len(self.levels)))]
         try:
             sort_order = np.lexsort(values)
@@ -846,7 +846,7 @@ def _try_mi(k):
 
             raise InvalidIndexError(key)
 
-    def _get_level_values(self, level, copy=True):
+    def _get_level_values(self, level):
         """
         Return vector of label values for requested level,
         equal to the length of the index
@@ -856,7 +856,6 @@ def _get_level_values(self, level, copy=True):
         Parameters
         ----------
         level : int level
-        copy  : bool whether copy of results should be done
 
         Returns
         -------
@@ -867,10 +866,7 @@ def _get_level_values(self, level, copy=True):
         labels = self.labels[level]
         filled = algos.take_1d(unique._values, labels,
                                fill_value=unique._na_value)
-        if copy:
-            values = unique._shallow_copy(filled)
-        else:
-            values = filled
+        values = unique._shallow_copy(filled)
         return values
 
     def get_level_values(self, level):
@@ -887,8 +883,8 @@ def get_level_values(self, level):
         values : Index
         """
         level = self._get_level_number(level)
-        values = self._get_level_values(level, copy=False)
-        return self.levels[level]._shallow_copy(values)
+        values = self._get_level_values(level)
+        return values
 
     def format(self, space=2, sparsify=None, adjoin=True, names=False,
                na_rep=None, formatter=None):