[Python-ideas] Potential PEP: with/except

[Barry Scott]

> On 22 Jan 2019, at 20:11, 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(...)
> 

Or this that shows the except/finally will be present?

try with open(path) as myfile:
   ... # Do stuff with file
except (OSError, IOError) as err:
   logger.error(...)

> 
> 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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