[Python-ideas] New Python syntax for continuing definitions for existing classes

[Chris Angelico]

On Wed, Sep 14, 2016 at 2:16 AM, Pim Schellart
<p.schellart at princeton.edu> wrote:
> Semantics
> =========
>
> The following two snippets are semantically identical::
>
>   continue class A:
>       x = 5
>       def foo(self):
>           pass
>       def bar(self):
>           pass
>
>   def foo(self):
>       pass
>   def bar(self):
>       pass
>   A.x = 5
>   A.foo = foo
>   A.bar = bar
>   del foo
>   del bar

Did you know that you can actually abuse decorators to do this with
existing syntax? Check out this collection of evil uses of decorators:

https://github.com/Rosuav/Decorators/blob/master/evil.py

I call them "evil" because they're potentially VERY confusing, but
they're not necessarily bad. The monkeypatch decorator does basically
what you're doing here, but with this syntax:

@monkeypatch
class A:
    x = 5
    def foo(self):
        pass
    def bar(self):
        pass

It's a little bit magical, in that it looks up the original class
using globals(); this is partly deliberate, as it means you can't
accidentally monkey-patch something from the built-ins, which will
either fail, or (far worse) succeed and confuse everyone.

ChrisA