On September 28, 2015 at 4:56:44 PM, Guido van Rossum (guido@python.org) wrote:
On Mon, Sep 28, 2015 at 1:41 PM, Donald Stufft wrote:
On September 28, 2015 at 4:25:12 PM, Guido van Rossum (guido@python.org) wrote:
On Mon, Sep 28, 2015 at 1:15 PM, Donald Stufft wrote:
The ? Modifying additional attribute accesses beyond just the immediate one bothers me too and feels more ruby than python to me.
Really? Have you thought about it?
Not extensively, mostly this is a gut feeling.
Suppose I have an object post which may be None or something with a tag attribute which should be a string. And suppose I want to get the lowercased tag, if the object exists, else None.
This seems a perfect use case for writing post?.tag.lower() -- this signifies that post may be None but if it exists, post.tag is not
to be None. So basically I want the equivalent of (post.tag.lower() if
expected post
is not None else None).
But if post?.tag.lower() were interpreted strictly as (post?.tag).lower(), then I would have to write post?.tag?.lower?(), which is an abomination. OTOH if post?.tag.lower() automatically meant post?.tag?.lower?() then I would silently get no error when post exists but post.tag is None (which in this example is an error).
Does ? propagate past a non None value? If it were post?.tag.name.lower() and post was not None, but tag was None would that be an error or would the ? propagate to the tag as well?
I was trying to clarify that by saying that foo?.bar.baz means (foo.bar.baz if foo is not None else None). IOW if tag was None that would be an error.
The rule then is quite simple: each ? does exactly one None check and divides the expression into exactly two branches -- one for the case where the thing preceding ? is None and one for the case where it isn't.
Ok, that makes me feel less bad than my initial impression was that ? was going to modify all following things so that they were all implicitly ?. Just splitting it into two different branches seems OK. I’m not a big fan of the punctuation though. It took me a minute to realize that post?.tag.lower() was saying if post is None, not if post.tag is None and I feel like it’s easy to miss the ?, especially when combined with other punctuation. ----------------- Donald Stufft PGP: 0x6E3CBCE93372DCFA // 7C6B 7C5D 5E2B 6356 A926 F04F 6E3C BCE9 3372 DCFA