[DB-SIG] When must transactions begin?

[M.-A. Lemburg]

Randall Nortman wrote:
> PEP 249 says that transactions end on commit() or rollback(), but it
> doesn't explicitly state when transactions should begin, and there is
> no begin() method. 

Transactions start implicitly after you connect and after you call
.commit() or .rollback(). They are not started for each statement.

> I think the implication is that transactions begin
> on the first execute(), but that's not explicitly stated.  At least
> one driver, pysqlite2/sqlite3, does not start a transaction for a
> SELECT statement.  It waits for a DML statement (INSERT, UPDATE,
> DELETE) before opening a transaction.  Other drivers open transactions
> on any statement, including SELECT.
> 
> My question for the DB-SIG is: Can I call it a bug in pysqlite2 that
> it does not open transactions on SELECT?  Should the spec be amended
> to make this explicit?  Or are both behaviors acceptable, in which
> case perhaps a begin() method needs to be added for when the user
> wants control over opening transactions?

I should probably add a note to PEP 249 about this.

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