BUG: fix isin with Series of tuples values (#16394) (#16434)

* Swiched out "values = np.array(list(values), dtype='object')" for "values = lib.list_to_object_array(list(values))" in the isin() method found in core/algorithms.py
Added test for comparing to a list of tuples

(cherry picked from commit e053ee3)

Author: jaredsnyder

doc/source/whatsnew/v0.20.2.txt

@@ -86,8 +86,6 @@ Reshaping
 - Bug in ``Series.isin(..)`` with a list of tuples (:issue:`16394`)
 - Bug in construction of a ``DataFrame`` with mixed dtypes including an all-NaT column. (:issue:`16395`)
 
-
-
 Numeric
 ^^^^^^^
 - Bug in .interpolate(), where limit_direction was not respected when limit=None (default) was passed (:issue:16282)

pandas/core/algorithms.py

@@ -388,7 +388,7 @@ def isin(comps, values):
                         "[{0}]".format(type(values).__name__))
 
     if not isinstance(values, (ABCIndex, ABCSeries, np.ndarray)):
-        values = np.array(list(values), dtype='object')
+        values = lib.list_to_object_array(list(values))
 
     comps, dtype, _ = _ensure_data(comps)
     values, _, _ = _ensure_data(values, dtype=dtype)

pandas/tests/frame/test_analytics.py

@@ -1201,6 +1201,14 @@ def test_isin_df(self):
         expected['B'] = False
         tm.assert_frame_equal(result, expected)
 
+    def test_isin_tuples(self):
+        # GH16394
+        df = pd.DataFrame({'A': [1, 2, 3], 'B': ['a', 'b', 'f']})
+        df['C'] = list(zip(df['A'], df['B']))
+        result = df['C'].isin([(1, 'a')])
+        tm.assert_series_equal(result,
+                               Series([True, False, False], name="C"))
+
     def test_isin_df_dupe_values(self):
         df1 = DataFrame({'A': [1, 2, 3, 4], 'B': [2, np.nan, 4, 4]})
         # just cols duped