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

doc/source/whatsnew/v0.24.0.txt

@@ -653,6 +653,7 @@ Indexing
 - Fixed ``DataFrame[np.nan]`` when columns are non-unique (:issue:`21428`)
 - 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`)
+- Bug in :func:`Index.__contains__` that returns True just in case val is float and dtype is integer, because float casted to integer (:issue:`22085`)
 
 Missing
 ^^^^^^^

pandas/core/indexes/base.py

@@ -1949,7 +1949,11 @@ 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 +2483,14 @@ 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
+        index = pd.Index([0, 1, 2, 3])
+
+        assert 1.1 not in index
+        assert 1.0 in index
+        assert 1 in index
+
 
 class TestIndexUtils(object):