[Python-ideas] Potential PEP: with/except

[Calvin Spealman]

On Tue, Jan 22, 2019 at 3:11 PM Paul Ferrell <pflarr at gmail.com> wrote:

> I've found that almost any time I'm writing a 'with' block, it's doing
> something that could throw an exception. As a result, each of those
> 'with' blocks needs to be nested within a 'try' block. Due to the
> nature of 'with', it is rarely (if ever) the case that the try block
> contains anything other than the with block itself.
>
> As a result, I would like to propose that the syntax for 'with' blocks
> be changed such that they can be accompanied by 'except', 'finally',
> and/or 'else' blocks as per a standard 'try' block. These would handle
> exceptions that occur in the 'with' block, including the execution of
> the applicable __enter__ and __exit__ methods.
>
> Example:
>
> try:
>     with open(path) as myfile:
>       ...   # Do stuff with file
> except (OSError, IOError) as err:
>     logger.error("Failed to read/open file {}: {}".format(path, err)
>
> The above would turn into simply:
>
> with open(path) as myfile:
>     ... # Do stuff with file
> except (OSError, IOError) as err:
>     logger.error(...)
>
>
It definitely makes sense, both the problem and the proposed solution.

The thing that concerns me is that any such problem and solution seems
to apply equally to any other kind of block. Why not allow excepts on fo
loops, for example?


>
> I think this is rather straightforward in meaning and easy to read,
> and simplifies some unnecessary nesting. I see this as the natural
> evolution of what 'with'
> is all about - replacing necessary try-finally blocks with something
> more elegant. We just didn't include the 'except' portion.
>
> I'm a bit hesitant to put this out there. I'm not worried about it
> getting shot down - that's kind of the point here. I'm just pretty
> strongly against to unnecessary syntactical additions to the language.
> This though, I think I can except. It introduces no new concepts and
> requires no special knowledge to use. There's no question about what
> is going on when you read it.
>
> --
> Paul Ferrell
> pflarr at gmail.com
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