Alternately, PEP 310 could be defined as equivalent to:
if hasattr(x, '__enter__'): x.__enter__() try: try: ... except: if hasattr(x, '__except__'): x.__except__(*sys.exc_info()) else: raise finally: x.__exit__()
In light of Alex's comments, I'd actually like to suggest the below as a potential new definition for PEP 310 (making __exit__ optional, and adding an __else__ handler):
if hasattr(x, '__enter__'):
x.__enter__()
try:
try:
# Contents of 'with' block
except:
if hasattr(x, '__except__'):
if not x.__except__(*sys.exc_info()): # [1]
raise
else:
raise
else:
if hasattr(x, '__else__'):
x.__else__()
finally:
if hasattr(x, '__exit__'):
x.__exit__()[1] A possible tweak to this line would be to have it swallow the exception by default (by removing the conditional reraise). I'd prefer to make the silencing of the exception explicit, by returning 'True' from the exception handling, and have 'falling off the end' of the exception handler cause the exception to propagate.
Whichever way that point goes, this definition would allow PEP 310 to handle Alex's example of factoring out standardised exception handling, as well as the original use case of resource cleanup, and the transaction handling:
class transaction(object):
def __enter__(self):
begin_transaction() def __except__(self, *exc_info):
abort_transaction() def __else__(self):
commit_transaction()
Cheers, Nick.
--
Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
---------------------------------------------------------------
http://boredomandlaziness.skystorm.net
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