[Tutor] associating two objects without ORM and processing a text file

[neubyr]

On Thu, Feb 14, 2013 at 4:05 PM, Dave Angel <davea at davea.name> wrote:

> On 02/14/2013 04:33 PM, Prasad, Ramit wrote:
>
>> Dave Angel wrote:
>>
>>> On 02/14/2013 12:35 PM, Prasad, Ramit wrote:
>>>
>>>> neubyr wrote:
>>>>
>>>>> I am not sure how to save an object in memory to a file before exiting
>>>>> the program. Any examples or
>>>>> related documentation links would be really helpful. I am guessing it
>>>>> would be using some kind of
>>>>> before teardown method, but not sure about it. Any help?
>>>>>
>>>>
>>>> Look at the pickle or shelve modules.
>>>> http://www.doughellmann.com/**PyMOTW/pickle/index.html<http://www.doughellmann.com/PyMOTW/pickle/index.html>
>>>> http://www.doughellmann.com/**PyMOTW/shelve/index.html<http://www.doughellmann.com/PyMOTW/shelve/index.html>
>>>>
>>>>
>>> You miss the point.  The OP wants to make sure the text file is saved no
>>> matter how the program happens to exit.  He's not asking how to format
>>> the file.
>>>
>>>
>> Hmm. Good point Dave, I did miss that point.
>>
>> My knee jerk response is a try/finally block, but I am sure there
>> are better ways.
>>
>> # UNTESTED
>> stored_data = {}
>> try:
>>      stored_data = load_data()
>>      while True:
>>          #<do program>
>> except Exception:
>>      raise # reraise exception to keep trace and still
>>            # propogate error for attention
>> finally:
>>      store_data(stored_data) # Save data since we are exiting
>>                              # (intentionally or not).
>>
>
> That would be my reaction as well.  I would, however make it conditional
> on some changes having been made.  That way if this program run only made
> queries, the effort and risk of saving can be avoided.
>
> The other thing I'd recommend is to store the data in an alternate file,
> and only delete the original when the alternate is ready to rename. That
> way, you can't readily get into trouble if something crashes while saving.
>
>
>
>
>
Thanks Ramit and Dave!

I haven't had chance to code/learn further, but I will give play with this
soon.

I do have a doubt regarding this - e.g. how would I implement this if my
program/application is web based. For example, loading the text file during
web server start and stop.

Hope to try it out soon!


- N
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