Default scope of variables

Frank Millman frank at chagford.com
Wed Jul 10 07:54:22 CEST 2013


"Ian Kelly" <ian.g.kelly at gmail.com> wrote in message 
news:CALwzidnf3Obe0eNf3xTHLj5a40K8HxVThVEipECQ8+34ZxyLxw at mail.gmail.com...
> On Tue, Jul 9, 2013 at 10:07 AM, Ethan Furman <ethan at stoneleaf.us> wrote:
>> You could also do it like this:
>>
>>     def updating(self):
>>         self.transaction_active = True
>>         return self
>
> Yes, that would be simpler.  I was all set to point out why this
> doesn't work, and then I noticed that the location of the
> "transaction_active" attribute is not consistent in the original code.
> The DbSession class places it on self, and then the example usage
> places it on the connection object (which I had based my version on).
> Since that seems to be a source of confusion, it demonstrates another
> reason why factoring this out is a good thing.

You had me worried there for a moment, as that is obviously an error.

Then I checked my actual code, and I find that I mis-transcribed it. It 
actually looks like this -

    with db_session as conn:
        db_session.transaction_active = True
        conn.cur.execute(...)

I am still not quite sure what your objection is to this. It feels 
straightforward to me.

Here is one possible answer. Whenever I want to commit a transaction I have 
to add the extra line. There is a danger that I could mis-spell 
'transaction_active', in which case it would not raise an error, but would 
not commit the transaction, which could be a hard-to-trace bug. Using your 
approach, if I mis-spelled 'db_session.connect()', it would immediately 
raise an error.

Is that your concern, or are there other issues?

Frank






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