M.-A. Lemburg writes:
> On 27.08.2020 17:53, David Mertz wrote:
> > Suppose we didn't have dict.get(). I would then probably write:
> >
> > val = mydict[key] if key in mydict else None
> >
> > Likewise, since we don't have list.get(), I would write:
> >
> > val = mylist[N] if len(mylist) >- N-1 else None
> >
> > Neither of those is impractical, but in both cases .get(key) seems to
> > express the intent in a more obvious way.
>
> Really ?
I think David is comparing the .get syntax to the if-else syntax.
First of all, he got the if-else wrong, which is a sign that .get is
easier to use, at least for writers and quite likely for readers.
Second I agree that ".get" is easier to read and understand
(especially with explicit default, as you advocate). It's even more
stark if you're after a component of the list element:
val = mylist[N if len(mylist) > N else default].content
vs.
val = mylist.get(N, default).content
> Let me try again :-)
>
> Getting an item from a bag of unknown items can easily fail,
> because you don't what's in the bag until you try to find
> the item.
>
> Trying to access an item from a non-existing bucket in an array
> will always fail. You know that in advance, since the bucket
> doesn't exist as per the array properties. You don't have to
> try finding it first.
But this isn't a C array. You don't know the length from the syntax.
So you have to "do work" to discover the bucket isn't there before you
access -- or you can delegate to the interpreter and catch IndexError.
Given how precise IndexError is (it only catches integer arguments
that fall outside the range of the array), I don't really see the
argument for refusing to encapsulate the try in a .get method, or that
its semantics differ from explicit bounds-checking.
It seems to me that you're expressing a preference for "look before
you leap" over "easier to ask forgiveness than permission" in the case
of array indicies, which is a stylistic thing. It's a style I prefer
in this case, but I can also see how other people would prefer a
different style, one that makes sense to encapsulate in .get. Is
there something more than stylistic preference that I'm missing?
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