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Re: Default scope of variables

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On 07/09/2013 01:38 AM, Frank Millman wrote:
>
> "Ian Kelly" <ian.g.kelly@gmail.com> wrote in message
> news:CALwzid=FzgjPebifx1stDBkh8iwLtWggwwPTPhZ1ykYg+05wEg@mail.gmail.com...
>> On Tue, Jul 9, 2013 at 1:35 AM, Frank Millman <frank@chagford.com> wrote:
>>> When any of them need any database access, whether for reading or for
>>> updating, they execute the following -
>>>
>>>      with db_session as conn:
>>>          conn.transaction_active = True  # this line must be added if
>>> updating
>>>          conn.cur.execute(__whatever__)
>>
>> I'd probably factor out the transaction_active line into a separate
>> DbSession method.
>>
>>     @contextmanager
>>     def updating(self):
>>         with self as conn:
>>             conn.transaction_active = True
>>             yield conn
>>
>> Then you can do "with db_session" if you're merely reading, or "with
>> db_session.updating()" if you're writing, and you don't need to repeat
>> the transaction_active line all over the place.
>>
>
> I'll bear it in mind, but I will have to expend some mental energy to
> understand it first <g>, so it will have to wait until I can find some time.

You could also do it like this:

     def updating(self):
         self.transaction_active = True
         return self

and a sample object:

     class Tester(object):
         def __init__(self):
             self.transaction_active = False
             print 'initializied'
         def __enter__(self, *args):
             print '__enter__: transaction_active =', self.transaction_active
             return self
         def __exit__(self, *args):
             self.transaction_active = False
             print '__exit__: transaction_active =', self.transaction_active
             return
         def updating(self):
             self.transaction_active = True
             print 'updating: self.transaction_active =', self.transaction_active
             return self

     with Tester() as conn:
         print 'in first with block'

     print '-' * 50

     with Tester().updating() as conn:
         print 'in second with block'

with it's test run:

     ethan@hydra:~$ python test_cm.py
     initialized
     __enter__: transaction_active = False
     in first with block
     __exit__: transaction_active = False
     --------------------------------------------------
     initialized
     updating: self.transaction_active = True
     __enter__: transaction_active = True
     in second with block
     __exit__: transaction_active = False

--
~Ethan~

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Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-04 03:27 +0000
  Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-04 14:07 +1000
    Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-04 05:32 +0000
      Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-04 15:47 +1000
        Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-04 16:38 +0000
          Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-05 02:58 +1000
          Re: Default scope of variables Wayne Werner <wayne@waynewerner.com> - 2013-07-07 08:13 -0500
          Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-07 23:43 +1000
            Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-07 16:03 +0000
              Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-08 10:46 +1000
            Re: Default scope of variables alex23 <wuwei23@gmail.com> - 2013-07-09 14:52 +1000
              Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-09 15:07 +1000
                Re: Default scope of variables alex23 <wuwei23@gmail.com> - 2013-07-09 16:08 +1000
                Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-09 16:13 +1000
                Re: Default scope of variables "Frank Millman" <frank@chagford.com> - 2013-07-09 09:35 +0200
                Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-09 17:45 +1000
                Re: Default scope of variables Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-09 01:56 -0600
                Re: Default scope of variables "Frank Millman" <frank@chagford.com> - 2013-07-09 10:22 +0200
                Re: Default scope of variables "Frank Millman" <frank@chagford.com> - 2013-07-09 10:38 +0200
                Re: Default scope of variables Ethan Furman <ethan@stoneleaf.us> - 2013-07-09 09:07 -0700
                Re: Default scope of variables Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-09 10:44 -0600
                Re: Default scope of variables Ethan Furman <ethan@stoneleaf.us> - 2013-07-09 10:23 -0700
                Re: Default scope of variables Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-09 12:41 -0600
                Re: Default scope of variables Ethan Furman <ethan@stoneleaf.us> - 2013-07-09 12:19 -0700
                Re: Default scope of variables "Frank Millman" <frank@chagford.com> - 2013-07-10 07:54 +0200
                Re: Default scope of variables Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-10 09:42 -0600
                Re: Default scope of variables Ethan Furman <ethan@stoneleaf.us> - 2013-07-10 08:29 -0700
                Re: Default scope of variables "Frank Millman" <frank@chagford.com> - 2013-07-11 07:52 +0200
          Re: Default scope of variables Ethan Furman <ethan@stoneleaf.us> - 2013-07-07 09:52 -0700
          Re: Default scope of variables Ethan Furman <ethan@stoneleaf.us> - 2013-07-07 11:59 -0700
          Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-08 10:48 +1000
            Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-08 02:23 +0000
              Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-08 13:11 +1000
                Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-08 05:00 +0000
                Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-08 15:14 +1000
      Re: Default scope of variables Peter Otten <__peter__@web.de> - 2013-07-04 08:48 +0200
      Re: Default scope of variables Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-04 01:12 -0600
      Re: Default scope of variables Dave Angel <davea@davea.name> - 2013-07-04 03:06 -0400
        Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-04 15:52 +0000
        Re: Default scope of variables Rotwang <sg552@hotmail.co.uk> - 2013-07-04 17:54 +0100
          Re: Default scope of variables Peter Otten <__peter__@web.de> - 2013-07-04 20:36 +0200
          Re: Default scope of variables Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-05 01:04 +0100
          Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-05 01:24 +0000
            Re: Default scope of variables Dave Angel <davea@davea.name> - 2013-07-04 22:03 -0400
            Re: Default scope of variables Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-05 03:29 +0100
            Re: Default scope of variables Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-05 03:27 +0100
            Re: Default scope of variables Rotwang <sg552@hotmail.co.uk> - 2013-07-05 07:28 +0100
        Re: Default scope of variables Neil Cerutti <neilc@norwich.edu> - 2013-07-05 13:24 +0000
          Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-05 23:43 +1000
            Re: Default scope of variables Neil Cerutti <neilc@norwich.edu> - 2013-07-05 15:36 +0000
          Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-07 16:08 +0000
            Re: Default scope of variables Neil Cerutti <neilc@norwich.edu> - 2013-07-08 11:54 +0000
              Re: Default scope of variables Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-08 14:14 +0100
      Re: Default scope of variables Lele Gaifax <lele@metapensiero.it> - 2013-07-04 14:43 +0200
      Re: Default scope of variables Wayne Werner <wayne@waynewerner.com> - 2013-07-04 10:45 -0500
  Re: Default scope of variables Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-04 05:30 +0100
    Re: Default scope of variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-04 05:45 +0000
  Re: Default scope of variables Chris Angelico <rosuav@gmail.com> - 2013-07-04 14:36 +1000
  Re: Default scope of variables Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-04 06:09 +0100
  Re: Default scope of variables Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-08 17:58 +0100

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