|Neil Toronto||Nov 19, 2007 10:59 am|
|Guido van Rossum||Nov 19, 2007 11:10 am|
|Luke Stebbing||Nov 19, 2007 12:20 pm|
|Neil Toronto||Nov 19, 2007 12:41 pm|
|Arnaud Delobelle||Nov 19, 2007 1:54 pm|
|Neil Toronto||Nov 19, 2007 2:03 pm|
|Greg Ewing||Nov 19, 2007 4:33 pm|
|Greg Ewing||Nov 19, 2007 5:23 pm|
|Luke Stebbing||Nov 19, 2007 5:27 pm|
|Luke Stebbing||Nov 19, 2007 5:49 pm|
|Neil Toronto||Nov 19, 2007 6:36 pm|
|Arnaud Delobelle||Nov 19, 2007 11:05 pm|
|ntoronto at cs.byu.edu||Nov 20, 2007 12:50 am|
|Jim Jewett||Nov 20, 2007 7:15 am|
|Greg Ewing||Nov 20, 2007 3:48 pm|
|Greg Ewing||Nov 20, 2007 4:42 pm|
|Ali Gholami Rudi||Nov 20, 2007 8:54 pm|
|Subject:||[Python-ideas] Explicit self argument, implicit super argument|
|From:||Guido van Rossum (gui...@python.org)|
|Date:||Nov 19, 2007 11:10:58 am|
The reason for explicit self in method definition signatures is semantic consistency. If you write
class C: def foo(self, x, y): ...
This really *is* the same as writing
class C: pass
def foo(self, x, y): ... C.foo = foo
And of course it works the other way as well: you really *can* invoke foo with an explicit argument for self as follows:
class D(C): ...
C.foo(D(), 1, 2)
IOW it's not an implementation hack -- it is a semantic device.
On Nov 19, 2007 11:00 AM, Neil Toronto <ntoronto at cs.byu.edu> wrote:
(Disclaimer: I have no issue with "self." and "super." attribute access, which is what most people think of when they think "implicit self".)
While showing a coworker a bytecode hack I made this weekend - it allows insertion of arbitrary function parameters into an already-existing function - he asked for a use case. I gave him this:
class A(object): # ... def method(x, y): self.x = x super.method(y)
where 'method' is replaced by this method wrapper via metaclass or decorator:
def method_wrapper(self, *args, **kwargs): return hacked_method(self, super(cls, self), *args, **kwargs)
These hackish details aren't important, the resulting "A.method" is.
It occurred to me that explicit self and implicit super is semantically inconsistent. Here's Python 3000's version of the above (please compare):
class A(object): def method(self, x, y): self.x = x super.method(y)
Why have a magic "super" local but not a magic "self" local? From a *general usage* standpoint, the only reason I can think of (which is not necessarily the only one, which is why I'm asking) is that a person might want to change the name of "self", like so:
class AddLike(object): # ... def __add__(a, b): # return something def __radd__(b, a): # return something
But reverse binary special methods are the only case where it's not extremely bad form. Okay, two reasons for explicit self: backward compatibility, but 2to3 would make it a non-issue.
From an *implementation standpoint*, making self implicit - a cell variable like super, for example - would wreak havoc with the current bound/unbound method distinction, but I'm not so sure that's a bad thing.
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-- --Guido van Rossum (home page: http://www.python.org/~guido/)