Move to instance properties

Author: TomAugspurger

pandas/core/indexes/base.py

@@ -244,12 +244,6 @@ class Index(IndexOpsMixin, PandasObject):
     _engine_type = libindex.ObjectEngine
 
     _accessors = set(['str'])
-    # Whether items can be selected from NDFrame.<item>
-    # Some indexes (DatetimeIndex, Int64Index) cannot contain
-    # valid Python identifiers. Setting _can_hold_identifiers = False is an
-    # optimization.
-    # https://github.com/pandas-dev/pandas/issues/19764
-    _can_hold_identifiers = True
 
     str = CachedAccessor("str", StringMethods)
 
@@ -2089,6 +2083,23 @@ def __getitem__(self, key):
         else:
             return result
 
+    @property
+    def _can_hold_identifiers(self):
+        """
+        Whether the Index class *can* hold Python identifiers.
+
+        This is useful for short-circuting lookups in NDFrame.__getattr__.
+        Some index-classes can't hold identifiers (NumericIndex,
+        DatetimeIndex), so there's no reason to search the index when a user
+        does `Series.foo<TAB>`.
+
+        Note that we don't care about `foo` here. This just a property
+        of the index class itself, nothing to do with an instance.
+
+        https://github.com/pandas-dev/pandas/issues/19764
+        """
+        return True
+
     def append(self, other):
         """
         Append a collection of Index options together

pandas/core/indexes/interval.py

@@ -207,7 +207,6 @@ class IntervalIndex(IntervalMixin, Index):
     _typ = 'intervalindex'
     _comparables = ['name']
     _attributes = ['name', 'closed']
-    _can_hold_identifiers = False  # can't contain Python identifiers
 
     # we would like our indexing holder to defer to us
     _defer_to_indexing = True
@@ -1304,6 +1303,12 @@ def __getitem__(self, value):
 
         return self._shallow_copy(left, right)
 
+    @property
+    def _can_hold_identifiers(self):
+        # perf: Intervals aren't valid Python identifiers.
+        # https://github.com/pandas-dev/pandas/issues/19764
+        return False
+
     # __repr__ associated methods are based on MultiIndex
 
     def _format_with_header(self, header, **kwargs):

pandas/core/indexes/numeric.py

@@ -31,7 +31,6 @@ class NumericIndex(Index):
 
     """
     _is_numeric_dtype = True
-    _can_hold_identifiers = False  # Can't contain Python identifiers
 
     def __new__(cls, data=None, dtype=None, copy=False, name=None,
                 fastpath=False):
@@ -115,6 +114,12 @@ def is_all_dates(self):
         """
         return False
 
+    @property
+    def _can_hold_identifiers(self):
+        # perf: Numeric elements are not valid identifiers.
+        # https://github.com/pandas-dev/pandas/issues/19764
+        return False
+
 
 _num_index_shared_docs['class_descr'] = """
     Immutable ndarray implementing an ordered, sliceable set. The basic object

pandas/core/indexes/period.py

@@ -204,7 +204,6 @@ class PeriodIndex(DatelikeOps, DatetimeIndexOpsMixin, Int64Index):
     """
     _typ = 'periodindex'
     _attributes = ['name', 'freq']
-    _can_hold_identifiers = False  # Can't contain Python identifiers
 
     # define my properties & methods for delegation
     _other_ops = []