ENH: avoid creating reference cycle on indexing (#15746)

asv_bench/benchmarks/indexing.py

@@ -287,3 +287,19 @@ def setup(self):
 
     def time_subset(self):
         self.p.ix[(self.inds, self.inds, self.inds)]
+
+
+class IndexerLookup(object):
+    goal_time = 0.2
+
+    def setup(self):
+        self.s = Series(range(10))
+
+    def time_lookup_iloc(self):
+        self.s.iloc
+
+    def time_lookup_ix(self):
+        self.s.ix
+
+    def time_lookup_loc(self):
+        self.s.loc

doc/source/whatsnew/v0.22.0.txt

@@ -67,7 +67,7 @@ Removal of prior version deprecations/changes
 Performance Improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
--
+- Indexers on Series or DataFrame no longer create a reference cycle (:issue:`17956`)
 -
 -
 

pandas/_libs/indexing.pyx

@@ -0,0 +1,22 @@
+# cython: profile=False
+
+cdef class _NDFrameIndexerBase:
+    '''
+    A base class for _NDFrameIndexer for fast instantiation and attribute
+    access.
+    '''
+    cdef public object obj, name, _ndim
+
+    def __init__(self, name, obj):
+        self.obj = obj
+        self.name = name
+        self._ndim = None
+
+    @property
+    def ndim(self):
+        # Delay `ndim` instantiation until required as reading it
+        # from `obj` isn't entirely cheap.
+        ndim = self._ndim
+        if ndim is None:
+            ndim = self._ndim = self.obj.ndim
+        return ndim

pandas/core/generic.py

@@ -1,5 +1,6 @@
 # pylint: disable=W0231,E1101
 import collections
+import functools
 import warnings
 import operator
 import weakref
@@ -1796,23 +1797,10 @@ def to_latex(self, buf=None, columns=None, col_space=None, header=True,
     @classmethod
     def _create_indexer(cls, name, indexer):
         """Create an indexer like _name in the class."""
-
         if getattr(cls, name, None) is None:
-            iname = '_%s' % name
-            setattr(cls, iname, None)
-
-            def _indexer(self):
-                i = getattr(self, iname)
-                if i is None:
-                    i = indexer(self, name)
-                    setattr(self, iname, i)
-                return i
-
+            _indexer = functools.partial(indexer, name)
             setattr(cls, name, property(_indexer, doc=indexer.__doc__))
 
-            # add to our internal names set
-            cls._internal_names_set.add(iname)
-
     def get(self, key, default=None):
         """
         Get item from object for given key (DataFrame column, Panel slice,

pandas/core/indexing.py

@@ -23,6 +23,7 @@
 from pandas.core.common import (is_bool_indexer, _asarray_tuplesafe,
                                 is_null_slice, is_full_slice,
                                 _values_from_object)
+from pandas._libs.indexing import _NDFrameIndexerBase
 
 
 # the supported indexers
@@ -85,19 +86,14 @@ class IndexingError(Exception):
     pass
 
 
-class _NDFrameIndexer(object):
+class _NDFrameIndexer(_NDFrameIndexerBase):
     _valid_types = None
     _exception = KeyError
     axis = None
 
-    def __init__(self, obj, name):
-        self.obj = obj
-        self.ndim = obj.ndim
-        self.name = name
-
     def __call__(self, axis=None):
         # we need to return a copy of ourselves
-        new_self = self.__class__(self.obj, self.name)
+        new_self = self.__class__(self.name, self.obj)
 
         if axis is not None:
             axis = self.obj._get_axis_number(axis)
@@ -1321,7 +1317,7 @@ class _IXIndexer(_NDFrameIndexer):
 
     """
 
-    def __init__(self, obj, name):
+    def __init__(self, name, obj):
 
         _ix_deprecation_warning = textwrap.dedent("""
             .ix is deprecated. Please use
@@ -1332,8 +1328,8 @@ def __init__(self, obj, name):
             http://pandas.pydata.org/pandas-docs/stable/indexing.html#ix-indexer-is-deprecated""")  # noqa
 
         warnings.warn(_ix_deprecation_warning,
-                      DeprecationWarning, stacklevel=3)
-        super(_IXIndexer, self).__init__(obj, name)
+                      DeprecationWarning, stacklevel=2)
+        super(_IXIndexer, self).__init__(name, obj)
 
     def _has_valid_type(self, key, axis):
         if isinstance(key, slice):

pandas/tests/indexing/test_indexing.py

@@ -5,6 +5,7 @@
 
 import pytest
 
+import weakref
 from warnings import catch_warnings
 from datetime import datetime
 
@@ -881,6 +882,14 @@ def test_partial_boolean_frame_indexing(self):
                                 columns=list('ABC'))
         tm.assert_frame_equal(result, expected)
 
+    def test_no_reference_cycle(self):
+        df = pd.DataFrame({'a': [0, 1], 'b': [2, 3]})
+        for name in ('loc', 'iloc', 'ix', 'at', 'iat'):
+            getattr(df, name)
+        wr = weakref.ref(df)
+        del df
+        assert wr() is None
+
 
 class TestSeriesNoneCoercion(object):
     EXPECTED_RESULTS = [

setup.py

@@ -335,6 +335,7 @@ class CheckSDist(sdist_class):
                  'pandas/_libs/index.pyx',
                  'pandas/_libs/algos.pyx',
                  'pandas/_libs/join.pyx',
+                 'pandas/_libs/indexing.pyx',
                  'pandas/_libs/interval.pyx',
                  'pandas/_libs/hashing.pyx',
                  'pandas/_libs/testing.pyx',
@@ -519,6 +520,7 @@ def pxd(name):
                    'depends': _pxi_dep['join']},
     '_libs.reshape': {'pyxfile': '_libs/reshape',
                       'depends': _pxi_dep['reshape']},
+    '_libs.indexing': {'pyxfile': '_libs/indexing'},
     '_libs.interval': {'pyxfile': '_libs/interval',
                        'pxdfiles': ['_libs/hashtable'],
                        'depends': _pxi_dep['interval']},