[issue31588] SystemError in class creation in case of a metaclass with a bad __prepare__() method

[Nick Coghlan]

Nick Coghlan <ncoghlan at gmail.com> added the comment:

There's no __prepare__ method in 2.7, so that version can't be affected by this.

For 3.6 and 3.7, I can't reproduce the reported SystemError. Instead, I get:

```
>>> class BadMetaclass(type):
...     def __prepare__(*args):
...         pass
... 
>>> class Foo(metaclass=BadMetaclass):
...     pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in Foo
TypeError: 'NoneType' object is not subscriptable

```

The error remains the same if I add `@classmethod` to the __prepare__ definition.


That's still thoroughly cryptic and worth changing, but indicates the test should be checking the error message details, not just the error type.

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versions:  -Python 2.7

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<https://bugs.python.org/issue31588>
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