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Date: Sun, 7 Jul 2013 23:43:24 +1000
Subject: Re: Default scope of variables
From: Chris Angelico <rosuav@gmail.com>
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On Sun, Jul 7, 2013 at 11:13 PM, Wayne Werner <wayne@waynewerner.com> wrote:
> Which you would then use like:
>
>
> conn = create_conn()
> with new_transaction(conn) as tran:
>      rows_affected = do_query_stuff(tran)
>      if rows_affected == 42:
>           tran.commit()

Yep. There's a problem, though, when you bring in subtransactions. The
logic wants to be like this:

with new_transaction(conn) as tran:
    tran.query("blah")
    with tran.subtransaction() as tran:
        tran.query("blah")
        with tran.subtransaction() as tran:
            tran.query("blah")
            # roll this subtransaction back
        tran.query("blah")
        tran.commit()
    tran.query("blah")
    tran.commit()

The 'with' statement doesn't allow this. I would need to use some kind
of magic to rebind the old transaction to the name, or else use a list
that gets magically populated:

with new_transaction(conn) as tran:
    tran[-1].query("blah")
    with subtransaction(tran):
        tran[-1].query("blah")
        with subtransaction(tran):
            tran[-1].query("blah")
            # roll this subtransaction back
        tran[-1].query("blah")
        tran[-1].commit()
    tran[-1].query("blah")
    tran[-1].commit()

I don't like the look of this. It might work, but it's hardly ideal.
This is why I like to be able to nest usages of the same name.

ChrisA