On Sat, May 18, 2019 at 8:17 PM Yonatan Zunger <zunger@humu.com> wrote:

Instead, we should permit any expression to be used. If a value does not expose an __enter__ method, it should behave as though its __enter__ method is return self; if it does not have an __exit__ method, it should behave as though that method is return False.

I'm not sure why you would want this. But it is really easy to implement with a named function already. I think it would be better to experiment with a wrapper function first, maybe put it on PyPI, before changing the language for something whose purpose is unclear (to me).

I think you probably mean something other than what you actually write. It doesn't really make sense for "any expression" as far as I can tell. What would it possibly mean to write:

with (2+2) as foo:

print(foo)

But anyway, my toy simple implementation which satisfies the stated requirement:

>>> from contextlib import contextmanager
>>> @contextmanager
... def zungerfy(obj):
... if hasattr(obj, '__enter__'):
... yield obj.__enter__()
... else:
... yield obj
... if hasattr(obj, '__exit__'):
... obj.__exit__()
...
>>> with zungerfy(Foo(42)) as foo:
... print("Hello", foo.val)
...
...
Hello 42
>>> with zungerfy(open('README.md')) as foo:
... print("Hello", foo.readline())

...
Hello ## About the course

Keeping medicines from the bloodstreams of the sick; food
from the bellies of the hungry; books from the hands of the
uneducated; technology from the underdeveloped; and putting
advocates of freedom in prisons. Intellectual property is
to the 21st century what the slave trade was to the 16th.