Closes #16613: Added optional mapping argument to ChainMap.new_child.

1 files changed, 8 insertions, 3 deletions

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index 53083e4bd6..0612e1f610 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -821,9 +821,14 @@ class ChainMap(MutableMapping):
 
     __copy__ = copy
 
-    def new_child(self):                        # like Django's Context.push()
-        'New ChainMap with a new dict followed by all previous maps.'
-        return self.__class__({}, *self.maps)
+    def new_child(self, m=None):                # like Django's Context.push()
+        '''
+        New ChainMap with a new map followed by all previous maps. If no
+        map is provided, an empty dict is used.
+        '''
+        if m is None:
+            m = {}
+        return self.__class__(m, *self.maps)
 
     @property
     def parents(self):                          # like Django's Context.pop()