[Python-ideas] Simple class initialization

[Steven D'Aprano]

Greg Ewing wrote:
> Steven D'Aprano wrote:
> 
>> That's not a bug, that's a feature.
>>
>> It's been stated many times by Guido that it's far too early to 
>> standardize on a single meaning for annotations.
> 
> I think it's a rather *strange* feature.
> 
> Imagine what would happen if someone other than Guido
> proposed a syntax extension with no defined semantics
> and no use cases. I don't think it would be very well
> received!

The benefits of being BDFL :)

But seriously, check the PEP: it's not written by Guido, and this 
feature is not driven by whim.

http://www.python.org/dev/peps/pep-3107/

Annotations have at least one good use-case, and the semantics are 
perfectly defined: annotations are arbitrary expressions, and they get 
stored in the function object in a known place. What you do with those 
annotations is up to you. That's no different from other general 
processes in Python, like name binding, class attributes, and function 
calling, which have open semantics.

("Okay, I've created a variable. What do I do with it now?" That's 
entirely up to you, Python won't tell you what to do next.)

The only difference is that those other processes are so well-known and 
have existed in some cases since the dawn of time (Fortran), and so we 
take them for granted. Annotations in the Python sense are new, and 
nobody knows what to do with them yet (except for the oh-so-predictable 
idea of type testing -- boring!).

I think its a brave and innovative move. If it's not successful, that 
says more about the conservativeness of Python programmers than the 
usefulness of the feature. I bet Perl coders would have found some way 
to make their code even more incomprehensible with it by now *grin*

More here on type checking in Python here:

http://lambda-the-ultimate.org/node/1519

In particular note the links to Guido's essays thinking aloud, which 
eventually lead to annotations.



-- 
Steven