[Python-ideas] Generator-based context managers can't skip __exit__

[Ethan Furman]

On 11/18/2016 12:42 PM, Ram Rachum wrote:

> Sure, here are a couple of use cases:
>
> 1. I'm making a program that lets people lease machines. They can issue
>  a command to lease 7 machines. When they do, my program leases them one
>  by one and adds them all to an exit stack, so in case there aren't 7
>  machines available, all the machines we leased get released and the
>  situation is back to normal. If everything goes fine, I do pop_all on
>  the exit stack so it doesn't get exited and the machines stay leased,
>  then the command exits and the user gets his machines.

So you're using the contextlib.ExitStack context manager?

> 2. I have a test suite that creates a temporary folder to put files that
>  are used by the test. The temporary folder is created by a context
>  manager that deletes it at the end. But, if the test fails I want to
>  move the temporary folder away into a dedicated folder for the user to
>  be able to examine those files later to figure out why the test fails.
>  So I want to tell the temporary folder context manager to not delete
>  the folder, because it'll fail since it was moved away so it's not at
>  the expected location.

My first thought is to make a custom context manager for this use-case, but if you really want to use a generator instead can't you just put in an existence check for the directory and only delete if it is still there?

--
~Ethan~