From 1e289f0436e51ec049421d580e60876d6cf73f98 Mon Sep 17 00:00:00 2001
From: MomIsBestFriend <>
Date: Wed, 25 Dec 2019 21:50:17 +0200
Subject: [PATCH 1/2] Orderdict -> defaultdict(list)

---
 pandas/core/groupby/generic.py | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index dc343f670b725..502a978f95bbe 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -5,7 +5,7 @@
 These are user facing as the result of the ``df.groupby(...)`` operations,
 which here returns a DataFrameGroupBy object.
 """
-from collections import OrderedDict, abc, namedtuple
+from collections import OrderedDict, abc, defaultdict, namedtuple
 import copy
 from functools import partial
 from textwrap import dedent
@@ -1894,12 +1894,10 @@ def _normalize_keyword_aggregation(kwargs):
     """
     # Normalize the aggregation functions as Mapping[column, List[func]],
     # process normally, then fixup the names.
-    # TODO(Py35): When we drop python 3.5, change this to
-    # defaultdict(list)
     # TODO: aggspec type: typing.OrderedDict[str, List[AggScalar]]
     # May be hitting https://github.com/python/mypy/issues/5958
     # saying it doesn't have an attribute __name__
-    aggspec = OrderedDict()
+    aggspec = defaultdict(list)
     order = []
     columns, pairs = list(zip(*kwargs.items()))
 

From f9d173c022727db588867e6cb75b03d070f41ab9 Mon Sep 17 00:00:00 2001
From: MomIsBestFriend <>
Date: Wed, 25 Dec 2019 23:38:07 +0200
Subject: [PATCH 2/2] CLN: Simplified code

---
 pandas/core/groupby/generic.py | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index 502a978f95bbe..713e52ce1d28f 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -1902,10 +1902,7 @@ def _normalize_keyword_aggregation(kwargs):
     columns, pairs = list(zip(*kwargs.items()))
 
     for name, (column, aggfunc) in zip(columns, pairs):
-        if column in aggspec:
-            aggspec[column].append(aggfunc)
-        else:
-            aggspec[column] = [aggfunc]
+        aggspec[column].append(aggfunc)
         order.append((column, com.get_callable_name(aggfunc) or aggfunc))
 
     # uniquify aggfunc name if duplicated in order list