[Python-ideas] AttributeError: __exit__

[Guido van Rossum]

Please file a bug.

On May 6, 2011 5:17 PM, "Daniel Holth" <dholth at gmail.com> wrote:
>
> I just learned about Python internals from The ZODB transaction module. In
Python < 2.7, the module works as a transaction manager. More or less:
>
> manager = Foo()
> __exit__ = manager.__exit__
> __enter__ = manager.__enter__
>
> After Python 2.7, it doesn't work.
>
> import transaction
> with transaction: pass
> >>> AttributeError: __exit__
>
> It should be obvious to even the most casual observer that the exception
is because, after Python 2.7, the with: statement has its own opcode that
bypasses transaction.__getattribute__('__exit__') ->
transaction.__dict__['__exit__']. Instead, CPython calls special_lookup(),
looks for __exit__ on the module type, not the instance, doesn't find it,
and raises the AttributeError.
>
> Instead,
>
> import sys
> sys.__exit__
> >>> AttributeError: 'module' object has no attribute '__exit__'
>
> The interpreter should at least explain the AttributeError in the same way
as it does when the user triggers it directly.
>
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