[Python-ideas] PEP 505 (None coalescing operators) thoughts

[Donald Stufft]

On September 28, 2015 at 4:25:12 PM, Guido van Rossum (guido at 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 expected
> to be None. So basically I want the equivalent of (post.tag.lower() if 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?


-----------------
Donald Stufft
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