From 832aa08afecee4f59cb480c4e4a6b29bcbb22b94 Mon Sep 17 00:00:00 2001
From: Simon Charette <simon.charette@zapier.com>
Date: Sun, 6 Oct 2019 13:56:15 +0200
Subject: [PATCH] Used defaultdict in deletion.Collector.

---
 django/db/models/deletion.py | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/django/db/models/deletion.py b/django/db/models/deletion.py
index ae82d26340..02dfc43e40 100644
--- a/django/db/models/deletion.py
+++ b/django/db/models/deletion.py
@@ -1,4 +1,5 @@
-from collections import Counter
+from collections import Counter, defaultdict
+from functools import partial
 from itertools import chain
 from operator import attrgetter
 
@@ -65,8 +66,9 @@ class Collector:
     def __init__(self, using):
         self.using = using
         # Initially, {model: {instances}}, later values become lists.
-        self.data = {}
-        self.field_updates = {}  # {model: {(field, value): {instances}}}
+        self.data = defaultdict(set)
+        # {model: {(field, value): {instances}}}
+        self.field_updates = defaultdict(partial(defaultdict, set))
         # fast_deletes is a list of queryset-likes that can be deleted without
         # fetching the objects into memory.
         self.fast_deletes = []
@@ -76,7 +78,7 @@ class Collector:
         # should be included, as the dependencies exist only between actual
         # database tables; proxy models are represented here by their concrete
         # parent.
-        self.dependencies = {}  # {model: {models}}
+        self.dependencies = defaultdict(set)  # {model: {models}}
 
     def add(self, objs, source=None, nullable=False, reverse_dependency=False):
         """
@@ -90,7 +92,7 @@ class Collector:
             return []
         new_objs = []
         model = objs[0].__class__
-        instances = self.data.setdefault(model, set())
+        instances = self.data[model]
         for obj in objs:
             if obj not in instances:
                 new_objs.append(obj)
@@ -101,8 +103,7 @@ class Collector:
         if source is not None and not nullable:
             if reverse_dependency:
                 source, model = model, source
-            self.dependencies.setdefault(
-                source._meta.concrete_model, set()).add(model._meta.concrete_model)
+            self.dependencies[source._meta.concrete_model].add(model._meta.concrete_model)
         return new_objs
 
     def add_field_update(self, field, value, objs):
@@ -113,9 +114,7 @@ class Collector:
         if not objs:
             return
         model = objs[0].__class__
-        self.field_updates.setdefault(
-            model, {}).setdefault(
-            (field, value), set()).update(objs)
+        self.field_updates[model][field, value].update(objs)
 
     def _has_signal_listeners(self, model):
         return (