API: change IntervalIndex.contains to work elementwise

pandas/core/indexes/base.py

@@ -4036,6 +4036,10 @@ def contains(self, key):
         .. deprecated:: 0.25.0
             Use ``key in index`` instead of ``index.contains(key)``.
         """
+        warnings.warn(
+            "The 'contains' method is deprecated and will be removed in a "
+            "future versions. Use 'key in index' instead of "
+            "'index.contains(key)", FutureWarning, stacklevel=2)
         return key in self
 
     def __hash__(self):

pandas/core/indexing.py

@@ -2393,7 +2393,7 @@ def convert_to_index_sliceable(obj, key):
     elif isinstance(key, str):
 
         # we are an actual column
-        if obj._data.items.contains(key):
+        if key in obj._data.items:
             return None
 
         # We might have a datetimelike string that we can translate to a

pandas/tests/indexes/test_base.py

@@ -2156,6 +2156,11 @@ def test_tab_complete_warning(self, ip):
             with provisionalcompleter('ignore'):
                 list(ip.Completer.completions('idx.', 4))
 
+    def test_deprecated_contains(self):
+        for index in self.indices.values():
+            with tm.assert_produces_warning(FutureWarning):
+                index.contains(1)
+
 
 class TestMixedIntIndex(Base):
     # Mostly the tests from common.py for which the results differ

pandas/tests/indexes/test_range.py

@@ -271,10 +271,12 @@ def test_cached_data(self):
         91 in idx
         assert idx._cached_data is None
 
-        idx.contains(90)
+        with tm.assert_produces_warning(FutureWarning):
+            idx.contains(90)
         assert idx._cached_data is None
 
-        idx.contains(91)
+        with tm.assert_produces_warning(FutureWarning):
+            idx.contains(91)
         assert idx._cached_data is None
 
         idx.all()