[Python-ideas] PEP 505: None-aware operators

[Rhodri James]

On 29/07/18 16:12, Abe Dillon wrote:
> spam?.eggs.cheese.aardvark  # why would you ever do this?

If you knew that if you really have something in "spam", your program 
guarantees it will have an "eggs" attribute with a "cheese" attribute, 
etc, you just don't know if "spam" is not None.  It's the same insider 
knowledge you would use if you wrote it out as

spam.eggs.cheese.aardvark if spam is not None else None

The same sort of knowledge of your program structure could lead to you 
to use "?." instead of "." in any place or places in the chain.  If your 
program gives you strong enough guarantees, it is the sort of thing you 
can use to reduce the code's workload.

By way of example, I was working on some C code last night that was 
expanding an internal buffer, possibly from non-existence.  It did lot 
of taking the difference between various pointers to determine how big 
the new buffer needed to be, how much to copy from the old buffer, etc. 
It looked rather hairy until you realised that the code gave a strong 
guarantee that either all the pointers were meaningful or they were all 
NULL, so the pointer differences always made sense.  I rewrote that code 
so that it didn't take differences of NULL pointers since that was what 
the bug specified, but honestly it looks lumpier and less clear now.  A 
big comment explaining what was going on would probably be better.

-- 
Rhodri James *-* Kynesim Ltd