gh-109022: [Enum] require `names=()` to create empty enum type (GH-109048)

add guard so that ``Enum('bar')`` raises a TypeError instead of
creating a new enum class called `bar`.  To create the new but
empty class, use:

    huh = Enum('bar', names=())

1 files changed, 5 insertions, 0 deletions

diff --git a/Lib/enum.py b/Lib/enum.py
index 4b99e7b..994a7b9 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -730,6 +730,11 @@ class EnumType(type):
                 value = (value, names) + values
             return cls.__new__(cls, value)
         # otherwise, functional API: we're creating a new Enum type
+        if names is None and type is None:
+            # no body? no data-type? possibly wrong usage
+            raise TypeError(
+                    f"{cls} has no members; specify `names=()` if you meant to create a new, empty, enum"
+                    )
         return cls._create_(
                 class_name=value,
                 names=names,