On Tue, Jul 30, 2019 at 1:13 AM Paul Moore p.f.moore@gmail.com wrote:
On Tue, 30 Jul 2019 at 04:00, Ethan Furman ethan@stoneleaf.us wrote:
If this "with...except" leads to more robust code then I think many would like to use it, but not if it's confusing as that would lead to less robust code.
For me, "it's for robust code" is sufficient hint that I now remember what it does (much the same way that "it's for search loops" is the hint I need for for...else). And when I'm trying to write robust code, I do worry about exceptions in the with expression, and the fact that I can't easily catch them. So for me, this is definitely a real (albeit one I can usually ignore) problem.
I'm not sure I understand the desire to catch every possible exception right where it occurs. I've never felt this need somehow. Apart from open() can someone give me an example from real code where a context manager is likely to raise an exception that can meaningfully be handled?
I've re-read Serhiy's original example, involving a context manager for connecting to a socket and a for-loop for reading the data from the socket and writing it to another one (all three operations that may fail), but I find it unconvincing. For reference I'm copying it here again:
with connect() as stream: # connect() or __enter__() can fail.
for data in stream: # __next__() can fail
write(data) # write() can fail
This very much looks like toy networking code to me -- real networking code
is always written in a completely different way, using different
abstractions that raise different exceptions, and I don't think it would be
written in this style even if with and for had optional
except
clauses. (Alternatively, you can write little wrappers that turn OSError
into different exceptions so you can use a single try/except/except/except
statement to handle them all.)
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