try pattern for database connection with the close method

[Ian Kelly]

On Sat, Feb 21, 2015 at 5:22 AM, Mark Lawrence <breamoreboy at yahoo.co.uk> wrote:
> On 21/02/2015 02:42, Mario Figueiredo wrote:
>>
>> Hello all,
>>
>> I'm using the following pattern for db access  that requires me to
>> close the connection as soon as it is not needed:
>>
>>          import sqlite3 as lite
>>
>>          try:
>>              db = lite.connect('data.db')
>>          except lite.DatabaseError:
>>              raise OSError('database file corrupt or not found.')
>>          else:
>>              try:
>>                  with db:
>>                      db.execute(sql, parms)
>>              except lite.IntegrityError:
>>                  raise ValueError('invalid data')
>>              finally:
>>                  db.close()
>>
>> Since it's a bit verbose, is there a better way?
>>
>> Note: The user of this API has the whole database functionality
>> abstracted away. Hence the exception channeling in the except clauses.
>>
>
> Use your context manager at the outer level.
>
> import sqlite3 as lite
>
> try:
>     with lite.connect('data.db') as db:
>     try:
>         db.execute(sql, parms)
>     except lite.IntegrityError:
>         raise ValueError('invalid data')
> except lite.DatabaseError:
>     raise OSError('database file corrupt or not found.')

This could result in the OSError being misleadingly raised due to some
DatabaseError raised by the execute rather than the connect.