[issue19025] Deleting attribute of Enum gives misleading error message

[Vajrasky Kok]

New submission from Vajrasky Kok:

>>> from enum import Enum
>>> class MyPet(Enum):
...   CUTE_CAT = 1
...   VIGOROUS_DOG = 2
...   UGLY_BLOBFISH = 3
...   PROMISCUOUS_BONOBO = 4
...   def spam(cls): pass
... 
>>> del MyPet.CUTE_CAT
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: CUTE_CAT

This is misleading. I have CUTE_CAT attribute in Enum. It should throw TypeError exception.

>>> del MyPet.LONELY_WOLF
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: LONELY_WOLF

This is correct.

>>> del MyPet['CUTE_CAT']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'EnumMeta' object does not support item deletion

I think this behaviour is correct.

>>> del MyPet['LONELY_WOLF']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'EnumMeta' object does not support item deletion

This behaviour is somewhat misleading. I don't have LONELY_WOLF item.

>>> del MyPet.spam
>>> hasattr(MyPet, 'spam')
False

This is correct. We should be able to delete method from Enum class, or shouldn't we?

>>> cute_cat = MyPet.CUTE_CAT
>>> del cute_cat.name
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/sky/Code/python/programming_language/cpython/Lib/enum.py", line 29, in __delete__
    raise AttributeError("can't delete attribute")
AttributeError: can't delete attribute

This is *maybe" correct. But shouldn't it be TypeError exception?

All the exception messages related with deleting attribute in Python codebase are using TypeError exception (with one exception in pyexpat on which it uses RuntimeError exception).

Attached the patch to handle the attribute deletion correctly.

For now, I don't change the exception for the last case (del MyPet.CUTE_CAT.name) because maybe there is an exception case for enum.

----------
components: Library (Lib)
files: handling_attribute_deletion_correctly_in_enum.patch
keywords: patch
messages: 197775
nosy: ethan.furman, vajrasky
priority: normal
severity: normal
status: open
title: Deleting attribute of Enum gives misleading error message
type: behavior
versions: Python 3.4
Added file: http://bugs.python.org/file31771/handling_attribute_deletion_correctly_in_enum.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue19025>
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