[Tutor] global exception handling?

[Che M]

> > But, the issue is, I have many places where I write to the database and would have to embed each of these in a try/except block.  I can do that, but wondered if there is a "global" way to catch this 'database is locked' error?  I found someone asking this sort of question online but it doesn't appear to be answered:
> > http://bytes.com/topic/python/answers/799486-how-do-i-prevent-exceptions-stopping-execution-global-exception-handler
> 
> I'm not sure why you would like to do that: your code assumes the database interaction works fine, and based on that just continues it's normal flow. If the database is locked, you'll need to do something to prevent your code crashing further down, which is what you put in the except OperationalError: block. I would assume that the error handling depends on where you are in the code.
> If you can always perform the same type of error handling, just create a convenience function (possibly with the SQL statement as argument) that calls the database and returns the results, and put the database call inside the try: except: clause. Then you need to do this only once.

Interesting, it didn't occur to me to do that.  I may give it a try.  Since I am making INSERTs and UPDATEs to the database from all over the application (in different modules), maybe I should put this error-handling convenience function in a module and import it into every other module, then I can just use it.  Unfortunately, I'll still have to go back and find every instance of when I do INSERT or UPDATE to change this to use the convenience function, but it will still save me some keystrokes to fix the app.

> A global way to catch the database-locked exception is just to put the try: except OperationalError: around your complete code. Exceptions propagate all the way to the function where your program started, and if you catch it there, you will catch every OperationalError exception from anywhere in the code. Of course, your program then always exits anyway, because you can't return to the point where the the exception was thrown (or maybe you can, but not that I'm aware of. I wouldn't recommend it though).

That I really didn't know at all.  But yes, if the program exits, that's not going to work.

> > > p.s. *I use the nice program SQLite Database Browser and if I edit a field in the database my Python app is accessing, click "Apply changes", but I do *not* save the changes (that is, I do not click the disk icon), when I go to write to that database from my Python app, I get a 'database is locked' error.

> Sounds like somewhat odd behaviour to me: "apply changes" for me means "apply & commit", ie, it includes the save operation. Might 
> just be me.  I guess "Apply changes" opens the database connection, but then "save" performs the actual commit to the database, and 
> in the meantime the database is locked.

I don't know, either, but I was glad to find a way to reproduce the problem so that I could anticipate it for potential users.

Thanks for your help,
Che
 		 	   		  
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