[Python-Dev] Multiline with statement line continuation
steve at pearwood.info
Sat Aug 16 13:16:52 CEST 2014
On Sat, Aug 16, 2014 at 05:25:33PM +1000, Ben Finney wrote:
> > they would have already mistaken:
> > with a, b, c: ...
> > the same way. But they haven't.
> Right. The presence or absence of parens make a big semantic difference.
from silly.mistakes.programmers.make import (
hands, up, anyone, who, thinks, this, is_, a, tuple)
def function(how, about, this, one): ...
But quite frankly, even if there is some person somewhere who gets
confused and tries to write:
context_managers = (open("a"), open("b", "w"), open("c", "w"))
with context_managers as things:
text = things.read()
I simply don't care. They will try it, discover that tuples are not
context managers, fix their code, and move on. (I've made sillier
mistakes, and became a better programmer from it.)
We cannot paralyse ourselves out of fear that somebody, somewhere, will
make a silly mistake. You can try that "with tuple" code right now, and
you will get nice runtime exception. I admit that the error message is
not the most descriptive I've ever seen, but I've seen worse, and any
half-decent programmer can do what they do for any other unexpected
exception: read the Fine Manual, or ask for help, or otherwise debug the
problem. Why should this specific exception be treated as so harmful
that we have to forgo a useful piece of functionality to avoid it?
Some designs are bug-magnets, like the infamous "except A,B" syntax,
which fails silently, doing the wrong thing. Unless someone has a
convincing rationale for how and why this multi-line with will likewise
be a bug-magnet, I don't think that some vague similarity between it and
tuples is justification for rejecting the proposal.
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