[Python-Dev] Re: PEP 318: Can't we all just get along?

[Bob Ippolito]

On Aug 19, 2004, at 3:30 PM, Paul Morrow wrote:

> James Y Knight wrote:
>
>> On Aug 19, 2004, at 7:45 AM, Paul Morrow wrote:
>>> The vast majority of instance methods I've seen all use 'self' as 
>>> the first parameter.  Likewise, most class methods use 'cls' or 
>>> 'klass' as their first parameter.  If we exploit these conventions, 
>>> we end up with a simple, clear, obvious mechanism for denoting (this 
>>> aspect of) a method's type.
>>>
>>>     class Foo(Object):
>>>         def m1(self, a, b):    # this is an instance method of Foo
>>>             pass
>>>
>>>         def m2(cls, a, b):     # this is a class method of Foo
>>>             pass
>>>
>>>         def m3(a, b):          # this is a static method of Foo
>>>             pass
>>>
>>> A special Object (capital 'O') class could work this magic so that 
>>> old code didn't break.
>>>
>>> I know that this is odd.  But then so are most of the great things 
>>> about Python.
>> You can do that today. See also 
>> http://www.python.org/pycon/dc2004/papers/48/conveniencytypes.py
>
> Aha!  Thanks!

Whatever happened to explicit is better than implicit?  ;)

>> However, note that IMO it is quite rude to use a metaclass (or your 
>> capital O object -- same thing) to do this, as it will break any 
>> objects inheriting from your class that don't expect the strange 
>> automatic behavior. This auto-class/staticmethod-ification should be 
>> local to your code, and thus is really a candidate for a class 
>> decorator.
>> @automethods
>> class Foo(object):
>>   ...
>
> But then wouldn't subclasses of Foo have the same rude behavior?  In 
> fact, isn't the use of any metaclass rude, by your definition, as it 
> will change the default class behavior in some way?

No, a decorator happens once.  A metaclass can/does have permanent 
effects and becomes an integral and/or annoying part of the inheritance 
graph.

class Foo(object):
     __metaclass__ = Bar
     ...

is *much* different than

class Foo(object):
     ...
Foo = barEquivalentFunction(Foo)

which is the same as

@barEquivalentFunction
class Foo(object):
     ...

-bob