BUG: .isin(...) now coerces sets to lists

pandas/core/algorithms.py

@@ -113,6 +113,8 @@ def isin(comps, values):
         raise TypeError("only list-like objects are allowed to be passed"
                         " to isin(), you passed a "
                         "[{0}]".format(type(values).__name__))
+    if com.is_set_like(values):
+        values = list(values)
 
     # GH11232
     # work-around for numpy < 1.8 and comparisions on py3

pandas/core/common.py

@@ -1765,6 +1765,10 @@ def is_list_like(arg):
             not isinstance(arg, compat.string_and_binary_types))
 
 
+def is_set_like(arg):
+    return (is_list_like(arg) and not hasattr(arg, '__getitem__'))
+
+
 def is_dict_like(arg):
     return hasattr(arg, '__getitem__') and hasattr(arg, 'keys')
 

pandas/tests/series/test_analytics.py

@@ -1118,6 +1118,9 @@ def test_isin_with_i8(self):
         result = s.isin([np.datetime64(s[1])])
         assert_series_equal(result, expected2)
 
+        result = s.isin(set(s[0:2]))
+        assert_series_equal(result, expected)
+
         # timedelta64[ns]
         s = Series(pd.to_timedelta(lrange(5), unit='d'))
         result = s.isin(s[0:2])

pandas/tests/test_common.py

@@ -571,6 +571,18 @@ def test_is_list_like():
         assert not com.is_list_like(f)
 
 
+def test_is_set_like():
+    passes = (set([1, 'a']), frozenset([1, 'a']))
+    fails = ([], [1], (1, ), (1, 2), {'a': 1}, Series([1]), Series([]),
+             Series(['a']).str, 1, '2', object())
+
+    for p in passes:
+        assert com.is_set_like(p)
+
+    for f in fails:
+        assert not com.is_set_like(f)
+
+
 def test_is_dict_like():
     passes = [{}, {'A': 1}, pd.Series([1])]
     fails = ['1', 1, [1, 2], (1, 2), range(2), pd.Index([1])]