Author ncoghlan
Recipients Julian, barry, benjamin.peterson, eric.araujo, ezio.melotti, georg.brandl, ishimoto, lukasz.langa, ncoghlan, pablogsal, r.david.murray, serhiy.storchaka, steven.daprano, ulope
Date 2018-09-28.14:48:19
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Message-id <1538146099.41.0.545547206417.issue12782@psf.upfronthosting.co.za>
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Especially since the dynamic flexibility of ExitStack comes at a genuine runtime cost when unwinding the resource stack.

I also (very!) belatedly noticed that I never answered Julian's request for clarification about the potential grammar ambiguity, so going into detail about that now:

The first item in the grammar after the 'with' keyword is a 'test' node, which can already start with a parenthesis, which means a naive attempt at allowing grouping parentheses will likely fail to generate a valid LL(1) parser.

That doesn't mean a more sophisticated change isn't possible (and Pablo has apparently implemented one) - it just means that the required grammar update is going to be more complicated than just changing:

    with_stmt: 'with' with_item (',' with_item)*  ':' suite

to be:

    with_stmt: 'with' (with_items | '(' with_items ')') ':' suite
    with_items: with_item (',' with_item)*

(That would need too much lookahead to decide whether an opening parenthesis belongs to the first 'with_item' in 'with_items' or if it's starting the alternative multi-line grouping construct)
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Date User Action Args
2018-09-28 14:48:19ncoghlansetrecipients: + ncoghlan, barry, georg.brandl, ishimoto, benjamin.peterson, ezio.melotti, eric.araujo, steven.daprano, r.david.murray, lukasz.langa, Julian, serhiy.storchaka, ulope, pablogsal
2018-09-28 14:48:19ncoghlansetmessageid: <1538146099.41.0.545547206417.issue12782@psf.upfronthosting.co.za>
2018-09-28 14:48:19ncoghlanlinkissue12782 messages
2018-09-28 14:48:19ncoghlancreate