CLN: Define and pin GroupBy properties without exec (pandas-dev#28651)

Author: jbrockmendel

ci/code_checks.sh

@@ -125,6 +125,10 @@ if [[ -z "$CHECK" || "$CHECK" == "patterns" ]]; then
     # invgrep -R --include="*.py*" -E "from numpy import nan " pandas  # GH#24822 not yet implemented since the offending imports have not all been removed
     RET=$(($RET + $?)) ; echo $MSG "DONE"
 
+    MSG='Check for use of exec' ; echo $MSG
+    invgrep -R --include="*.py*" -E "[^a-zA-Z0-9_]exec\(" pandas
+    RET=$(($RET + $?)) ; echo $MSG "DONE"
+
     MSG='Check for pytest warns' ; echo $MSG
     invgrep -r -E --include '*.py' 'pytest\.warns' pandas/tests/
     RET=$(($RET + $?)) ; echo $MSG "DONE"
@@ -184,7 +188,7 @@ if [[ -z "$CHECK" || "$CHECK" == "patterns" ]]; then
     invgrep -R --include="*.rst" ".. ipython ::" doc/source
     RET=$(($RET + $?)) ; echo $MSG "DONE"
 
-    MSG='Check that no file in the repo contains tailing whitespaces' ; echo $MSG
+    MSG='Check that no file in the repo contains trailing whitespaces' ; echo $MSG
     set -o pipefail
     if [[ "$AZURE" == "true" ]]; then
         # we exclude all c/cpp files as the c/cpp files of pandas code base are tested when Linting .c and .h files

pandas/core/groupby/generic.py

@@ -11,7 +11,7 @@
 from functools import partial
 from textwrap import dedent
 import typing
-from typing import Any, Callable, FrozenSet, Iterator, Sequence, Type, Union
+from typing import Any, Callable, FrozenSet, Sequence, Type, Union
 import warnings
 
 import numpy as np
@@ -70,47 +70,63 @@
 ScalarResult = typing.TypeVar("ScalarResult")
 
 
-def whitelist_method_generator(
-    base_class: Type[GroupBy], klass: Type[FrameOrSeries], whitelist: FrozenSet[str]
-) -> Iterator[str]:
+def generate_property(name: str, klass: Type[FrameOrSeries]):
     """
-    Yields all GroupBy member defs for DataFrame/Series names in whitelist.
+    Create a property for a GroupBy subclass to dispatch to DataFrame/Series.
+
+    Parameters
+    ----------
+    name : str
+    klass : {DataFrame, Series}
+
+    Returns
+    -------
+    property
+    """
+
+    def prop(self):
+        return self._make_wrapper(name)
+
+    parent_method = getattr(klass, name)
+    prop.__doc__ = parent_method.__doc__ or ""
+    prop.__name__ = name
+    return property(prop)
+
+
+def pin_whitelisted_properties(klass: Type[FrameOrSeries], whitelist: FrozenSet[str]):
+    """
+    Create GroupBy member defs for DataFrame/Series names in a whitelist.
 
     Parameters
     ----------
-    base_class : Groupby class
-        base class
     klass : DataFrame or Series class
         class where members are defined.
-    whitelist : frozenset
+    whitelist : frozenset[str]
         Set of names of klass methods to be constructed
 
     Returns
     -------
-    The generator yields a sequence of strings, each suitable for exec'ing,
-    that define implementations of the named methods for DataFrameGroupBy
-    or SeriesGroupBy.
+    class decorator
 
+    Notes
+    -----
     Since we don't want to override methods explicitly defined in the
     base class, any such name is skipped.
     """
-    property_wrapper_template = """@property
-def %(name)s(self) :
-    \"""%(doc)s\"""
-    return self.__getattr__('%(name)s')"""
-
-    for name in whitelist:
-        # don't override anything that was explicitly defined
-        # in the base class
-        if hasattr(base_class, name):
-            continue
-        # ugly, but we need the name string itself in the method.
-        f = getattr(klass, name)
-        doc = f.__doc__
-        doc = doc if type(doc) == str else ""
-        wrapper_template = property_wrapper_template
-        params = {"name": name, "doc": doc}
-        yield wrapper_template % params
+
+    def pinner(cls):
+        for name in whitelist:
+            if hasattr(cls, name):
+                # don't override anything that was explicitly defined
+                #  in the base class
+                continue
+
+            prop = generate_property(name, klass)
+            setattr(cls, name, prop)
+
+        return cls
+
+    return pinner
 
 
 class NDFrameGroupBy(GroupBy):
@@ -747,13 +763,9 @@ def filter(self, func, dropna=True, *args, **kwargs):
         return self._apply_filter(indices, dropna)
 
 
+@pin_whitelisted_properties(Series, base.series_apply_whitelist)
 class SeriesGroupBy(GroupBy):
-    #
-    # Make class defs of attributes on SeriesGroupBy whitelist
-
     _apply_whitelist = base.series_apply_whitelist
-    for _def_str in whitelist_method_generator(GroupBy, Series, _apply_whitelist):
-        exec(_def_str)
 
     @property
     def _selection_name(self):
@@ -1368,15 +1380,11 @@ def pct_change(self, periods=1, fill_method="pad", limit=None, freq=None):
         return (filled / shifted) - 1
 
 
+@pin_whitelisted_properties(DataFrame, base.dataframe_apply_whitelist)
 class DataFrameGroupBy(NDFrameGroupBy):
 
     _apply_whitelist = base.dataframe_apply_whitelist
 
-    #
-    # Make class defs of attributes on DataFrameGroupBy whitelist.
-    for _def_str in whitelist_method_generator(GroupBy, DataFrame, _apply_whitelist):
-        exec(_def_str)
-
     _block_agg_axis = 1
 
     _agg_see_also_doc = dedent(

pandas/core/groupby/groupby.py

@@ -562,8 +562,6 @@ def __getattr__(self, attr):
             return object.__getattribute__(self, attr)
         if attr in self.obj:
             return self[attr]
-        if hasattr(self.obj, attr):
-            return self._make_wrapper(attr)
 
         raise AttributeError(
             "%r object has no attribute %r" % (type(self).__name__, attr)