I think I like it. Q. Safe to assume this would catch exceptions from both the call to `open` as well as the call to `open.__enter__`? Q. What about something even more verbose (descriptive) like`try with open(...) as cfg:`? 🙂 Paul On Thu, 2021-04-08 at 15:59 +0100, anthony.flury via Python-ideas wrote:
We are all familiar with the `with` statement for context managers, so that the resources are correctly finalized/closed in case of an exception either in terms of the resources being allocated of the processing. It is very common though to wrap the `with block` in an outer `try` block, since although we know that the resource has been closed, at an 'application' level it is still neccessary to deal with the exception - an example might be :
try: with open('config.cfg', 'r') as cfg: # Process the open file config = load_config(cfg) except FileNotFound: logging.info('Config file not found - using default configuration') except PermissionError: logging.warning('Cannot open config .cfg - using default configuration') config = default_config() else: logging.info('Using config from config.cfg')
It struck me that this is probably quite a common idiom, and we have the main processing (of the opened resources) indented twice just to accommodate the outer try block. I was wondering whether a worthwhile extension might be to allow the `with` statement to have an `except` and `else` clauses which would have the same semantics as wrapping the `with` block with a try - for example the above would now look like:
with open('config.cfg', 'r') as cfg: # Process the open file config = load_config(cfg) except FileNotFound: logging.info('Config file not found - using default configuration') except PermissionError: logging.warning('Cannot open config .cfg - using default configuration') config = default_config() else: logging.info('Using config from config.cfg')
Treating the 'with' as an implied `try` would reduce the march to the right - now the key processing of the resource is now indented only one level - and the association of the exception from the `with` block is syntactically clear. I am not good enough with core development to put together a working prototype, but I can imagine that this simple extension would be worth while, but I would be more than happy to author a PEP for this if it gets some initial positive feedback. Open questions - that I have - should we allow `except`, `else` and `finally` clauses (or just `except` and `else` - do we need `finally` here). -- Anthony Flury Moble: +44 07743 282707 Home: +44 (0)1206 391294 email: anthony.flury@btinternet.com _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/ITNCZD... Code of Conduct: http://python.org/psf/codeofconduct/