bpo-37479: on Enum subclasses with mixins, __format__ uses overridden __str__ (GH-14545)

* bpo-37479: on Enum subclasses with mixins, __format__ uses overridden __str__
diff --git a/Misc/ACKS b/Misc/ACKS
index a4d4372..36fe727 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -356,6 +356,7 @@
 Raúl Cumplido
 Antonio Cuni
 Brian Curtin
+Jason Curtis
 Paul Dagnelie
 Lisandro Dalcin
 Darren Dale
diff --git a/Misc/NEWS.d/next/Library/2019-07-02-12-43-57.bpo-37479.O53a5S.rst b/Misc/NEWS.d/next/Library/2019-07-02-12-43-57.bpo-37479.O53a5S.rst
new file mode 100644
index 0000000..cf23155
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-07-02-12-43-57.bpo-37479.O53a5S.rst
@@ -0,0 +1,2 @@
+When `Enum.__str__` is overridden in a derived class, the override will be
+used by `Enum.__format__` regardless of whether mixin classes are present.
\ No newline at end of file