From 1a459eebf4b85bd6e07543e3a0deec3bb85d2411 Mon Sep 17 00:00:00 2001
From: "Vgr E. Barry" <vgr255@live.ca>
Date: Wed, 25 Apr 2018 20:39:57 -0400
Subject: [PATCH] Add ability to delete items only if they exist from UserDict

---
 src/containers.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/containers.py b/src/containers.py
index bd397d5..d911982 100644
--- a/src/containers.py
+++ b/src/containers.py
@@ -314,6 +314,12 @@ class UserDict(dict):
                 value.dict_values.append(self)
 
     def __delitem__(self, item):
+        if isinstance(item, slice): # special-case: delete if it exists, otherwise don't
+            if item.start is item.step is None: # checks out
+                item = item.stop
+                if item not in self:
+                    return
+
         value = self[item]
         super().__delitem__(item)
         if isinstance(item, User):