On 2/1/2021 7:54 PM, Skip Montanaro wrote:
However... Network applications being what they are, hiccups are going
to happen. In the time since I swapped in the imapclient package, I've
also had to catch exceptions raised by lower level modules/packages I
wasn't using directly, discovering them only as they occurred. (Think
of it as lazy exception discovery. I suppose if I was developing the
application for others, I'd have been more proactive about uncovering
the exceptions.) In addition to a couple imapclient exceptions, I also
now need to catch socket.gaierror, ConnectionError and
imaplib.IMAP4.error.
Here's the crux of the problem. Where does responsibility generally
fall for low level exception handling?
The general advice on this list is 'Only catch exceptions you can
usefully do something with'. Some things are clear. Any code calling
next(it) should catch possible StopIteration. Library code, like
IMAPClient, should not catch BaseException and reraise SystemExit.
Other times, 'useful' is not so clear.
I don't mean to pick on IMAPClient.
It's pypi page https://pypi.org/project/IMAPClient/
has author and maintainer email links. You can ask them what their
intention is in regard to dependency exceptions. Their feature list
includes "Exceptions are raised when errors occur." Does this include
letting the exceptions you mention, and others, pass through? Do you
think their doc should be any clearer than it is?
I think responsibility partly depends on whether a particular low level
exception is a flow control exception or bug exception, and if the
latter, in whose code.
It's just a recent example and got me thinking about the
problem. Is it (generally) the responsibility of the application
author or the package author? This isn't an issue just for network
applications with a number of moving parts (socket, ssl, higher level
packages, etc). It happens in almost all applications or packages,
even if it's just to deal with exceptions raised by internal data
structures.
--
Terry Jan Reedy
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