On 2020-08-06 22:52, Chris Angelico wrote:
On Fri, Aug 7, 2020 at 11:01 AM Jonathan Grant
<jonathanallengr...@gmail.com> wrote:
How can we start to revive this PEP? And I completely agree, making the syntax
`... except ... with ...` is much better than `eor`.
Have a read of the PEP's rejection notice at the top. To revive the
PEP, the objections to it need to be solved.
It seems that the rationale that was used in the PEP was fairly
narrowly focused on the comparison with things like dict.get() and the
idea of EAFP. A somewhat broader justification might be something along
these lines:
In practice, a sizable number of try/except statements do nothing except
evaluate a single expression and assign it to a variable in the try
block, with a single except block that instead assigns a different value
to the same variable. This requires four lines of code even if the
expression and exception-set involved are quite simple.
This common pattern is Python's current way of expressing the idea of "I
want this, or, if that doesn't work, then this other thing", where
"doesn't work" means "raises a certain exception". This is parallel to
the if-else ternary operator, but the condition "raises an exception"
cannot currently be described with an expression, so if-else cannot be
used to handle this case.
Many well-designed functions raise exceptions to signal well-defined
error conditions for which the calling code has an easily-expressed
alternative value (i.e., "what to use instead of the return value of the
function, if it raises like this"). In other words, both the
exceptional condition and the desired result when it occurs may be
expressed clearly and briefly --- except that it can't, because the
try/except structure needed to shim in the alternative is itself so
cumbersome. Similarly, in many such situations, the variable assigned
inside the try/except is only used once immediately after, and the whole
if-this-except-this logic could have been inlined into the following
code, if not for the fact that try/except is a statement.
This PEP proposes a clean and simple way to handle this common
situation. Just as the if-else ternary operator provides a handy way to
encode "X unless condition A, in which case Y", the except operator
provides a handy way to encode "X unless EXCEPTIONAL condition A, in
which case Y".
--
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is no
path, and leave a trail."
--author unknown
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-le...@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/XD35QJMO62KBK4I6P7VVA74NWOF7XKY5/
Code of Conduct: http://python.org/psf/codeofconduct/
