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Fri Apr 22 19:11:25 CEST 2005 · https://mail.python.org/pipermail/python-dev/2005-April/052852.html

Nick Coghlan wrote:
> An alternative would be to replace the 'yield None' with a 'break' or
> 'continue', and create an object which supports the resource protocol
> and NOT the iterator protocol. Something like:
> 
> def my_resource():
>   print "Hi!"   # Do entrance code
>   continue      # Go on with the contents of the 'with' block
>   print "Bye!"  # Do exit code
> 
> (This is currently a SyntaxError, so it isn't ambiguous in any way)

That's a very interesting suggestion.  I've been lurking, thinking about
a way to use something like PEP 310 to help manage database
transactions.  Here is some typical code that changes something under
transaction control:

    begin_transaction()
    try:
        changestuff()
        changemorestuff()
    except:
        abort_transaction()
        raise
    else:
        commit_transaction()

There's a lot of boilerplate code there.  Using your suggestion, I could
write that something like this:

    def transaction():
        begin_transaction()
        try:
            continue
        except:
            abort_transaction()
            raise
        else:
            commit_transaction()

    with transaction():
        changestuff()
        changemorestuff()

Shane

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