BUG: Fix Index construction when given empty generator (pandas-dev#21470).

Author: Liam3851

pandas/core/indexes/base.py

@@ -429,15 +429,18 @@ 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 is_list_like(data) and data:
+            if tupleize_cols and is_list_like(data):
+                # GH21470: convert iterable to list before determining if empty 
                 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):
-                    from .multi import MultiIndex
-                    return MultiIndex.from_tuples(
-                        data, names=name or kwargs.get('names'))
+
+                if data:
+                    # we must be all tuples, otherwise don't construct
+                    # 10697
+                    if all(isinstance(e, tuple) for e in data):
+                        from .multi import MultiIndex
+                        return MultiIndex.from_tuples(
+                            data, names=name or kwargs.get('names'))
             # other iterable of some kind
             subarr = com._asarray_tuplesafe(data, dtype=object)
             return Index(subarr, dtype=dtype, copy=copy, name=name, **kwargs)

pandas/tests/indexes/test_base.py

@@ -438,14 +438,22 @@ def test_constructor_dtypes_timedelta(self, attr, klass):
         result = klass(list(values), dtype=dtype)
         tm.assert_index_equal(result, index)
 
-    def test_constructor_empty_gen(self):
+    def test_constructor_empty_list(self):
         skip_index_keys = ["repeats", "periodIndex", "rangeIndex",
                            "tuples"]
         for key, index in self.generate_index_types(skip_index_keys):
             empty = index.__class__([])
             assert isinstance(empty, index.__class__)
             assert not len(empty)
 
+    def test_constructor_empty_gen(self):
+        skip_index_keys = ["repeats", "periodIndex", "rangeIndex",
+                           "tuples"]
+        for key, index in self.generate_index_types(skip_index_keys):
+            empty = index.__class__(x for x in [])
+            assert isinstance(empty, index.__class__)
+            assert not len(empty)
+
     @pytest.mark.parametrize("empty,klass", [
         (PeriodIndex([], freq='B'), PeriodIndex),
         (RangeIndex(step=1), pd.RangeIndex),