REF/PERF: dont use hashtable in IndexEngine.__contains__ (#45192)

Author: jbrockmendel

pandas/_libs/index.pyx

@@ -128,10 +128,12 @@ cdef class IndexEngine:
         self._np_type = values.dtype.type
 
     def __contains__(self, val: object) -> bool:
-        # We assume before we get here:
-        #  - val is hashable
-        self._ensure_mapping_populated()
-        return val in self.mapping
+        hash(val)
+        try:
+            self.get_loc(val)
+        except KeyError:
+            return False
+        return True
 
     cpdef get_loc(self, object val):
         # -> Py_ssize_t | slice | ndarray[bool]
@@ -141,7 +143,7 @@ cdef class IndexEngine:
         if is_definitely_invalid_key(val):
             raise TypeError(f"'{val}' is an invalid key")
 
-        self._check_type(val)
+        val = self._check_type(val)
 
         if self.over_size_threshold and self.is_monotonic_increasing:
             if not self.is_unique:
@@ -270,6 +272,7 @@ cdef class IndexEngine:
 
     cdef _check_type(self, object val):
         hash(val)
+        return val
 
     @property
     def is_mapping_populated(self) -> bool:

pandas/_libs/index_class_helper.pxi.in

@@ -35,6 +35,10 @@ cdef class {{name}}Engine(IndexEngine):
     cdef _check_type(self, object val):
     {{if name not in {'Float64', 'Float32'} }}
         if not util.is_integer_object(val):
+            if util.is_float_object(val):
+                # Make sure Int64Index.get_loc(2.0) works
+                if val.is_integer():
+                    return int(val)
             raise KeyError(val)
         {{if name.startswith("U")}}
         if val < 0:
@@ -46,6 +50,7 @@ cdef class {{name}}Engine(IndexEngine):
             # in particular catch bool and avoid casting True -> 1.0
             raise KeyError(val)
     {{endif}}
+        return val
 
 
 {{endfor}}

pandas/core/indexes/base.py

@@ -6422,8 +6422,6 @@ def _maybe_cast_indexer(self, key):
         If we have a float key and are not a floating index, then try to cast
         to an int if equivalent.
         """
-        if not self.is_floating():
-            return com.cast_scalar_indexer(key)
         return key
 
     def _maybe_cast_listlike_indexer(self, target) -> Index:

pandas/core/indexes/numeric.py

@@ -25,7 +25,6 @@
 
 from pandas.core.dtypes.common import (
     is_dtype_equal,
-    is_float,
     is_float_dtype,
     is_integer_dtype,
     is_numeric_dtype,
@@ -213,22 +212,6 @@ def _ensure_dtype(cls, dtype: Dtype | None) -> np.dtype | None:
             # dtype for Int64Index, UInt64Index etc. Needed for backwards compat.
             return cls._default_dtype
 
-    def __contains__(self, key) -> bool:
-        """
-        Check if key is a float and has a decimal. If it has, return False.
-        """
-        if not is_integer_dtype(self.dtype):
-            return super().__contains__(key)
-
-        hash(key)
-        try:
-            if is_float(key) and int(key) != key:
-                # otherwise the `key in self._engine` check casts e.g. 1.1 -> 1
-                return False
-            return key in self._engine
-        except (OverflowError, TypeError, ValueError):
-            return False
-
     # ----------------------------------------------------------------
     # Indexing Methods