BUG: support tupleization for mixed levels

closes #18505

Author: toobaz

doc/source/whatsnew/v0.22.0.txt

@@ -147,6 +147,7 @@ Indexing
 - Bug in :func:`DataFrame.groupby` where tuples were interpreted as lists of keys rather than as keys (:issue:`17979`, :issue:`18249`)
 - Bug in :func:`MultiIndex.remove_unused_levels`` which would fill nan values (:issue:`18417`)
 - Bug in :func:`MultiIndex.from_tuples`` which would fail to take zipped tuples in python3 (:issue:`18434`)
+- Bug in :class:`Index`` construction from list of mixed type tuples (:issue:`18505`)
 - Bug in :class:`IntervalIndex` where empty and purely NA data was constructed inconsistently depending on the construction method (:issue:`18421`)
 - Bug in ``IntervalIndex.symmetric_difference()`` where the symmetric difference with a non-``IntervalIndex`` did not raise (:issue:`18475`)
 

pandas/core/base.py

@@ -874,8 +874,9 @@ def _map_values(self, mapper, na_action=None):
                 # convert to an Series for efficiency.
                 # we specify the keys here to handle the
                 # possibility that they are tuples
-                from pandas import Series
-                mapper = Series(mapper, index=mapper.keys())
+                from pandas import Series, Index
+                index = Index(mapper, tupleize_cols=False)
+                mapper = Series(mapper, index=index)
 
         if isinstance(mapper, ABCSeries):
             # Since values were input this means we came from either

pandas/core/indexes/base.py

@@ -353,22 +353,15 @@ def __new__(cls, data=None, dtype=None, copy=False, name=None,
         elif data is None or is_scalar(data):
             cls._scalar_data_error(data)
         else:
-            if (tupleize_cols and isinstance(data, list) and data and
-                    isinstance(data[0], tuple)):
-
+            if tupleize_cols and is_list_like(data) and data:
+                if is_iterator(data):
+                    data = list(data)
                 # we must be all tuples, otherwise don't construct
                 # 10697
                 if all(isinstance(e, tuple) for e in data):
-                    try:
-                        # must be orderable in py3
-                        if compat.PY3:
-                            sorted(data)
-                        from .multi import MultiIndex
-                        return MultiIndex.from_tuples(
-                            data, names=name or kwargs.get('names'))
-                    except (TypeError, KeyError):
-                        # python2 - MultiIndex fails on mixed types
-                        pass
+                    from .multi import MultiIndex
+                    return MultiIndex.from_tuples(
+                        data, names=name or kwargs.get('names'))
             # other iterable of some kind
             subarr = _asarray_tuplesafe(data, dtype=object)
             return Index(subarr, dtype=dtype, copy=copy, name=name, **kwargs)

pandas/tests/indexes/test_base.py

@@ -106,6 +106,16 @@ def test_construction_list_mixed_tuples(self):
         assert isinstance(idx2, Index)
         assert not isinstance(idx2, MultiIndex)
 
+    @pytest.mark.parametrize('na_value', [None, np.nan])
+    @pytest.mark.parametrize('vtype', [list,
+                                       tuple,
+                                       lambda l: (x for x in l)])
+    def test_construction_list_tuples_nan(self, na_value, vtype):
+        # GH 18505 : valid tuples containing NaN
+        values = [(1, 'two'), (3., na_value)]
+        idx = Index(vtype(values))
+        assert isinstance(idx, MultiIndex)
+
     def test_constructor_from_index_datetimetz(self):
         idx = pd.date_range('2015-01-01 10:00', freq='D', periods=3,
                             tz='US/Eastern')