Add typing information

Author: topper-123

pandas/core/groupby/base.py

@@ -3,8 +3,14 @@
 hold the whitelist of methods that are exposed on the
 SeriesGroupBy and the DataFrameGroupBy objects.
 """
+from typing import FrozenSet, TYPE_CHECKING, Iterator, Type, Union
+
 from pandas.core.dtypes.common import is_list_like, is_scalar
 
+if TYPE_CHECKING:
+    from pandas import DataFrame, Series
+    from .groupby import GroupBy
+
 
 class GroupByMixin:
     """
@@ -88,19 +94,21 @@ def _gotitem(self, key, ndim, subset=None):
                                    'idxmax'])
 
 
-def whitelist_method_generator(base, klass, whitelist):
+def whitelist_method_generator(base: 'Type[GroupBy]',
+                               klass: 'Union[Type[DataFrame], Type[Series]]',
+                               whitelist: FrozenSet[str],
+                               ) -> Iterator[str]:
     """
     Yields all GroupBy member defs for DataFrame/Series names in whitelist.
 
     Parameters
     ----------
-    base : class
+    base : Groupby class
         base class
-    klass : class
+    klass : DataFrame or Series class
         class where members are defined.
-        Should be Series or DataFrame
-    whitelist : list
-        list of names of klass methods to be constructed
+    whitelist : frozenset
+        Set of names of klass methods to be constructed
 
     Returns
     -------