Phillip J. Eby wrote:
> Of course, it's not *really* that simple, because __try__ doesn't exactly
> correspond to 'try:', and it has to return something, but it sure is
> simpler than the mental gymnastics I'd go through to convert
> except/else/finally into "if" statements inside an __exit__.
You don't need to make that translation, though. Instead, you can just reraise
the passed in exception inside the __exit__() method:
def __exit__(self, *exc_info):
try:
try:
if exc_info:
raise exc_info[0], exc_info[1], exc_info[2]
except:
pass
else:
pass
finally:
pass
However, the __exit__() method does allow you to switch to using if statements
if that makes more sense (or would be more efficient). For instance, these are
possible __exit__ methods for a locking() statement template and a transaction()
statement template:
# locking's exit method
def __exit__(self, *exc_info):
self.lock.release()
if exc_info:
raise exc_info[0], exc_info[1], exc_info[2]
# transaction's exit method
def __exit__(self, *exc_info):
if exc_info:
self.db.rollback()
raise exc_info[0], exc_info[1], exc_info[2]
else:
self.db.commit()
I've posted draft 1.4 of my PEP 310/PEP 340 merger PEP (PEP 650, maybe?):
http://members.iinet.net.au/~ncoghlan/public/pep-3XX.html
This version cleans up the semantics a lot, so that the examples actually work
as intended, and there is One Obvious Way to do things like suppressing
exceptions (i.e. don't reraise them in the __exit__() method). It also
specifically addresses the question of using two methods in the protocol versus
four, and shows how an arbitrary try statement can be converted to a statement
template.
Cheers,
Nick.
--
Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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