[Python-3000] PEP 3119 - Introducing Abstract Base Classes (original) (raw)

Jim Jewett jimjjewett at gmail.com
Tue May 1 01:37:25 CEST 2007

On 4/30/07, Barry Warsaw <barry at python.org> wrote:

On Apr 27, 2007, at 1:10 PM, Jim Jewett wrote: > On 4/27/07, Barry Warsaw <barry at python.org> wrote:

>> Finally, I'm concerned with the "weight" of adding ABCs to all the >> built-in types.

> What if the builtin types did not initially derive from any ABC, but > were added (through an issubclass override) when the abc module was > imported?

That would allow for some unfortunately global side-effects. Say I happen to import your library that imports abc. Now all the built-in types in my entire application get globally changed. I'm also not sure how you'd implement that.

I don't see how these side-effects could ever be detected, except to the extent that issubclass overrides are inherently dangerous.

I see it something like

module abc.py

class Integer()... ...

Integer.register(int) Integer.register(long)

After that, int (and long) are changed only by the addition of an extra reference count; their bases and mro are utterly unchanged. But

isinstance(int, Integer)

is now True. Yes, this is global -- but the only way to detect it is to have a reference to Integer, which implies having already relied on the ABC framework.

-jJ

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