[Python-Dev] PEP 340 -- loose ends

[Shane Hathaway]

Reinhold Birkenfeld wrote:
> Noam Raphael wrote:
> 
>>On 5/4/05, Reinhold Birkenfeld <reinhold-birkenfeld-nospam at wolke7.net> wrote:
>>>resource = opening("file.txt")
>>>resource:
>>>    (...)
>>>
>>>The latter would have to be forbidden.
>>
>>Can you explain why it would have to be forbidden please?
> 
> 
> Well, with it you could create suites with _any_ introducing
> identifier. Consider:
> [...]
> 
> transaction:
>     (...)
> 
> 
> Do you understand my concern? It would be very, very hard to discern
> these "user-defined statements" from real language constructs.

For each block statement, it is necessary to create a *new* iterator,
since iterators that have stopped are required to stay stopped.  So at a
minimum, used-defined statements will need to call something, and thus
will have parentheses.  The parentheses might be enough to make block
statements not look like built-in keywords.

PEP 340 seems to punish people for avoiding the parentheses:

    transaction = begin_transaction()

    transaction:
        db.execute('insert 3 into mytable')

    transaction:
        db.execute('insert 4 into mytable')

I expect that only '3' would be inserted in mytable.  The second use of
the transaction iterator will immediately raise StopIteration.

Shane