Modernize `test_enum` by removing unused exception handling

[sobolevn]

Right now there are places in test_enum that for some reason contain code like

cpython/Lib/test/test_enum.py

Lines 53 to 76 in 4ff5690

	try:
	class IntStooges(int, Enum):
	LARRY = 1
	CURLY = 2
	MOE = 3
	except Exception as exc:
	IntStooges = exc
	try:
	class FloatStooges(float, Enum):
	LARRY = 1.39
	CURLY = 2.72
	MOE = 3.142596
	except Exception as exc:
	FloatStooges = exc
	try:
	class FlagStooges(Flag):
	LARRY = 1
	CURLY = 2
	MOE = 4
	BIG = 389
	except Exception as exc:
	FlagStooges = exc

For some reason we try to catch exceptions that won't ever happen (at least, they never should happen).

But, there are also regular Enums that are defined without any exceptions:

cpython/Lib/test/test_enum.py

Lines 78 to 101 in 4ff5690

	class FlagStoogesWithZero(Flag):
	NOFLAG = 0
	LARRY = 1
	CURLY = 2
	MOE = 4
	BIG = 389
	class IntFlagStooges(IntFlag):
	LARRY = 1
	CURLY = 2
	MOE = 4
	BIG = 389
	class IntFlagStoogesWithZero(IntFlag):
	NOFLAG = 0
	LARRY = 1
	CURLY = 2
	MOE = 4
	BIG = 389
	# for pickle test and subclass tests
	class Name(StrEnum):
	BDFL = 'Guido van Rossum'
	FLUFL = 'Barry Warsaw'

This is an artifact of 10+ age: 6b3d64a#diff-8467f9fbbff81abf26d87a8dbbf0e0c866157971948010e48cc73539251a9e4cR14

I propose to remove this and backport this PR to all supported Python versions.
PR will be available quite soon :)

Linked PRs

• gh-105522: Correctly handle possible exceptions in Enum creation in test_enum #105523

[ethanfurman]

@sobolevn You are correct that they never should happen, but if they do none of the tests in the file will run, so there will be no information on which tests did pass.

Rather than get rid of the existing exception handling, please update the global enums that do not have it (and their tests, of course).

[sobolevn]

Ok, if that's easier for you to work on / debug enum.py. I will update the PR shortly.

[sobolevn]

I finally had time to look at this. Here are my thoughts.

Raising an error for "protected" Enum

I've added these lines to EnumType.__prepare__:

if 'FloatStooges' in cls:
    raise RuntimeError('Example with FloatStooges', cls)

Here are the results:

======================================================================
ERROR: test_floatenum_fromhex (test.test_enum.TestSpecial.test_floatenum_fromhex)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_enum.py", line 1268, in test_floatenum_fromhex
    h = float.hex(FloatStooges.MOE.value)
                  ^^^^^^^^^^^^^^^^
AttributeError: 'RuntimeError' object has no attribute 'MOE'

======================================================================
ERROR: test_pickle_float (test.test_enum.TestSpecial.test_pickle_float)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_enum.py", line 1429, in test_pickle_float
    raise FloatStooges
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_enum.py", line 62, in <module>
    class FloatStooges(float, Enum):
  File "/Users/sobolev/Desktop/cpython/Lib/enum.py", line 494, in __prepare__
    raise RuntimeError('Example with FloatStooges', cls)
RuntimeError: ('Example with FloatStooges', 'FloatStooges')

----------------------------------------------------------------------

I've noticed that around 10 tests do not reraise errors if *Stooges is an exception instance.

Raising an error for an "unprotected" Enum

I went with IntFlagStoogesWithZero, so the whole suite failed with an error.

0:00:00 load avg: 0.91 [1/1] test_enum
test test_enum crashed -- Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/libregrtest/runtest.py", line 373, in _runtest_inner
    refleak = _runtest_inner2(ns, test_name)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/sobolev/Desktop/cpython/Lib/test/libregrtest/runtest.py", line 313, in _runtest_inner2
    the_module = importlib.import_module(abstest)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/sobolev/Desktop/cpython/Lib/importlib/__init__.py", line 88, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1293, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1266, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1237, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 841, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 996, in exec_module
  File "<frozen importlib._bootstrap>", line 400, in _call_with_frames_removed
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_enum.py", line 91, in <module>
    class IntFlagStoogesWithZero(IntFlag):
  File "/Users/sobolev/Desktop/cpython/Lib/enum.py", line 494, in __prepare__
    raise RuntimeError('Example with IntFlagStoogesWithZero', cls)
RuntimeError: ('Example with IntFlagStoogesWithZero', 'IntFlagStoogesWithZero')

test_enum failed (uncaught exception)

== Tests result: FAILURE ==

1 test failed:
    test_enum

Total duration: 49 ms
Tests result: FAILURE

Conclusion

Indeed, the first case is much more informative and helpful. But, I need to:

1. Update all "unprotected" enum definions
2. Reraise exception whenever any of these enums are used in tests