BUG: Check types in Index.__contains__ (#22085)

doc/source/whatsnew/v0.24.0.txt

@@ -658,6 +658,7 @@ Indexing
 - Bug when indexing :class:`DatetimeIndex` with nanosecond resolution dates and timezones (:issue:`11679`)
 - Bug where indexing with a Numpy array containing negative values would mutate the indexer (:issue:`21867`)
 - ``Float64Index.get_loc`` now raises ``KeyError`` when boolean key passed. (:issue:`19087`)
+- Bug in `scalar in Index` if scalar is a float while the Index is of integer dtype (:issue:`22085`)
 
 Missing
 ^^^^^^^

pandas/core/indexes/base.py

@@ -1993,7 +1993,11 @@ def __nonzero__(self):
     def __contains__(self, key):
         hash(key)
         try:
-            return key in self._engine
+            if (is_float(key) and is_integer_dtype(self.dtype) and
+                    int(key) != key):
+                return False
+            else:
+                return key in self._engine
         except (OverflowError, TypeError, ValueError):
             return False
 

pandas/tests/indexes/test_base.py

@@ -2483,6 +2483,19 @@ def test_comparison_tzawareness_compat(self, op):
         # TODO: implement _assert_tzawareness_compat for the reverse
         # comparison with the Series on the left-hand side
 
+    def test_contains_with_float_val(self):
+        # GH#22085
+        index1 = pd.Index([0, 1, 2, 3])
+        index2 = pd.Index([0.1, 1.1, 2.2, 3.3])
+
+        assert 1.1 not in index1
+        assert 1.0 in index1
+        assert 1 in index1
+
+        assert 1.1 in index2
+        assert 1.0 not in index2
+        assert 1 not in index2
+
 
 class TestIndexUtils(object):