Trying to instantiate an enum with an invalid value results in "During handling of the above exception, another exception occurred:". $ cat > test.py << EOF from enum import Enum class Color(Enum): RED = 1 GREEN = 2 BLUE = 3 Color(0) EOF $ python --version Python 3.8.1 $ python test.py ValueError: 0 is not a valid Color During handling of the above exception, another exception occurred: Traceback (most recent call last): File "test.py", line 8, in <module> Color(0) File "/usr/lib/python3.8/enum.py", line 304, in __call__ return cls.__new__(cls, value) File "/usr/lib/python3.8/enum.py", line 595, in __new__ raise exc File "/usr/lib/python3.8/enum.py", line 579, in __new__ result = cls._missing_(value) File "/usr/lib/python3.8/enum.py", line 608, in _missing_ raise ValueError("%r is not a valid %s" % (value, cls.__name__)) ValueError: 0 is not a valid Color I think this might be related to 019f0a0cb85e ("bpo-34536: raise error for invalid _missing_ results (GH-9147)"), but I haven't been able to confirm.

I can't reproduce this on the latest python (3.9) from master. Can you?

Never mind, I was able to reproduce it.

 New changeset c95ad7a91fbd7636f33a098d3b39964ab083bf49 by Ethan Furman in branch 'master': bpo-39728: Enum: fix duplicate `ValueError` (GH-22277) https://github.com/python/cpython/commit/c95ad7a91fbd7636f33a098d3b39964ab083bf49 

 New changeset a9ba8ba9a71f3cb8d274c354ff67b6206abeb8ac by Ethan Furman in branch '3.9': [3.9] bpo-39728: Enum: fix duplicate `ValueError` (GH-22277) (GH-22282) https://github.com/python/cpython/commit/a9ba8ba9a71f3cb8d274c354ff67b6206abeb8ac 

 New changeset 5efb1a77e75648012f8b52960c8637fc296a5c6d by Ethan Furman in branch '3.8': [3.8] bpo-39728: Enum: fix duplicate `ValueError` (GH-22277) (GH-22283) https://github.com/python/cpython/commit/5efb1a77e75648012f8b52960c8637fc296a5c6d