why are people still using classic classes?

[Simon Wittber]

I've noticed that a few ASPN cookbook recipes, which are recent
additions, use classic classes.

I've also noticed classic classes are used in many places in the
standard library.

I've been using new-style classes since Python 2.2, and am suprised
people are still using the classic classes.

Is there a legitimate use for classic classes that I am not aware of?
Is there a project to specifically migrate standard library classes to
new-style classes?

Sw.

 

[Roy Smith]

Is there a legitimate use for classic classes that I am not aware of?

Is there a reason NOT to use them? If a classic class works fine, what
incentive is there to switch to new style classes? I realize it's not
much effort to put "(object)" after your class name, but I'm lazy and
don't bother. I don't see how I've been hurt by that.

Obviously, if there was some feature of new style classes I wanted to
use, it would be a different story.

 

[Simon Wittber]

Is there a reason NOT to use them? If a classic class works fine, what

incentive is there to switch to new style classes?

Perhaps classic classes will eventually disappear? It seems strange
(and is difficult to explain to my peers) that a language offers two
different ways to define a standard class.

Sw.

 

[John Roth]

I've noticed that a few ASPN cookbook recipes, which are recent
additions, use classic classes.

I've also noticed classic classes are used in many places in the
standard library.

I've been using new-style classes since Python 2.2, and am suprised
people are still using the classic classes.

Is there a legitimate use for classic classes that I am not aware of?
Is there a project to specifically migrate standard library classes to
new-style classes?

Part of it is simply that it's a bit easier: you don't have to
inherit from object.

AFAIK, there's no project to migrate the standard library, and I'm
not at all sure that would be a good idea since existing programs
that asssume classic class behavior would be affected when
classes they inherited from suddenly changed.

Classic classes will go away sometime in the future, currently
planned for the semi-mythical 3.0 release.

John Roth

 

[Paul Rubin]

Is there a legitimate use for classic classes that I am not aware of?

Yes, new-style classes don't work in older Python installations. Some
Python users prefer not to be on such a frequent upgrade treadmill, so
they continue to use old versions. Therefore, anyone writing Python
code for wide distribution should avoid using new-style classes (and
other new Python features) unless they have a good reason.

 

[Paul Rubin]

Perhaps classic classes will eventually disappear?

It just means that the formerly "classic" syntax will define a
new-style class. Try to write code that works either way.

It would be nice if a __future__ directive were added right now (if
it's not there already) that processes all class definitions as
new-style. Otherwise there's no easy way to test for compatibility.

 

[Aahz]

Is there a legitimate use for classic classes that I am not aware of?
Is there a project to specifically migrate standard library classes to
new-style classes?

Exceptions, in addition to the other excellent reasons you've been
provided.

 

[Bengt Richter]

It just means that the formerly "classic" syntax will define a
new-style class. Try to write code that works either way.

It would be nice if a __future__ directive were added right now (if
it's not there already) that processes all class definitions as
new-style. Otherwise there's no easy way to test for compatibility.

UIAM, it's not so bad:
<type 'type'>

So I guess you can put __metaclass__ = type where you would have done the __future__ thing.

If you want to do a special metaclass thing (even using a proper class ;-),
you can override the global __metaclass__
... __metaclass__ = MC
... pass
...
('F', (), {'__module__': '__main__', '__metaclass__': <function MC at 0x02EE8D4C>})

Regards,
Bengt Richter

 

[Tim Roberts]

I've noticed that a few ASPN cookbook recipes, which are recent
additions, use classic classes.

I've also noticed classic classes are used in many places in the
standard library.

I've been using new-style classes since Python 2.2, and am suprised
people are still using the classic classes.

Is there a legitimate use for classic classes that I am not aware of?
Is there a project to specifically migrate standard library classes to
new-style classes?

Probably because there is still no compelling reason to break the old
habits and type those 6 extra characters.

Once a person has a case where the new classes make a difference, I suspect
they catch the new habit and never look back. I haven't crossed that
threshhold yet.

 

[Peter Hansen]

It just means that the formerly "classic" syntax will define a
new-style class. Try to write code that works either way.

Unfortunately, if we should follow the recent advice about
always using "super()" in the __init__ method, it's hard
to do what you suggest (though it sounds like good advice)
without resorting to extreme ugliness:
.... def __init__(self):
.... super(Classic, self).__init__()
....Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in __init__
TypeError: super() argument 1 must be type, not classobj

Could classic classes ever be removed without us having manually
to fix all __init__ calls to the superclass?

-Peter

 

[Aahz]

Unfortunately, if we should follow the recent advice about always using
"super()" in the __init__ method, it's hard to do what you suggest
(though it sounds like good advice) without resorting to extreme
ugliness:

... def __init__(self):
... super(Classic, self).__init__()
...
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in __init__
TypeError: super() argument 1 must be type, not classobj

Could classic classes ever be removed without us having manually
to fix all __init__ calls to the superclass?

Maybe. If you follow the python-dev thread about "super() considered
harmful", you'll learn that Guido believes super() should only be used
with class hierarchies explicitly designed for the purpose. Given that,
you'd have to do a lot of other changes to support super() and it's less
outrageous.

 

[Simon Wittber]

Unfortunately, if we should follow the recent advice about

always using "super()" in the __init__ method, it's hard
to do what you suggest (though it sounds like good advice)
without resorting to extreme ugliness:

'import this' also provides some good advice:

"There should be one-- and preferably only one --obvious way to do it."

It seems to me that python is not as simple/clean as it once was. It
has grown warts, for the sake of backwards compatibility.

Sw.

 

[Aahz]

'import this' also provides some good advice:

"There should be one-- and preferably only one --obvious way to do it."

It seems to me that python is not as simple/clean as it once was. It
has grown warts, for the sake of backwards compatibility.

That's progress. One of the primary goals for Python 3.0 is to make a
fresh start by removing a lot of the backwards compatibility.

 

[Michael Hobbs]

I've noticed that a few ASPN cookbook recipes, which are recent
additions, use classic classes.

I've also noticed classic classes are used in many places in the
standard library.

I've been using new-style classes since Python 2.2, and am suprised
people are still using the classic classes.

Is there a legitimate use for classic classes that I am not aware of?
Is there a project to specifically migrate standard library classes to
new-style classes?

I'm guessing that the biggest contributor to the continued prevalence
of classic classes is the official Python Tutorial:
http://docs.python.org/tut/node11.html#SECTION0011300000000000000000

I came into Python around the 2.2 timeframe and used the tutorial as
my starting point. I had often read people referring to "classic
classes" but assumed that it was some old pre-2.2 thing that I need
not worry about. For the longest time, I had assumed that I was using
new style classes because I created them exactly as prescribed in the
2.2 tutorial (which still hasn't changed for 2.3 or 2.4).

Now, classic classes are my habit and I see no compelling reason to
put in the effort to change my habits.

Regards,
- Mike

 

[Jarek Zgoda]

It just means that the formerly "classic" syntax will define a
new-style class. Try to write code that works either way.

Ideally, I'd like to have them working like in Delphi, where it doesn't
matter if you declare it as TSomeClass(TObject) or simply TSomeClass, it
is assumed that class is inherited from TObject if no other class is
specified.

 

[Steve Holden]

Unfortunately, if we should follow the recent advice about
always using "super()" in the __init__ method, it's hard
to do what you suggest (though it sounds like good advice)
without resorting to extreme ugliness:

.... def __init__(self):
.... super(Classic, self).__init__()
....
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in __init__
TypeError: super() argument 1 must be type, not classobj

Could classic classes ever be removed without us having manually
to fix all __init__ calls to the superclass?

That's not really an issue unless there's a diamond-shaped inheritance
graph and linearisation of the the super classes is required to ensure
that things stay sane. Remembering that the MO for classic classes and
types are rather different, how many cases do you think it will matter?

regards
Steve

 

[Steve Holden]

I'm guessing that the biggest contributor to the continued prevalence
of classic classes is the official Python Tutorial:
http://docs.python.org/tut/node11.html#SECTION0011300000000000000000

I came into Python around the 2.2 timeframe and used the tutorial as
my starting point. I had often read people referring to "classic
classes" but assumed that it was some old pre-2.2 thing that I need
not worry about. For the longest time, I had assumed that I was using
new style classes because I created them exactly as prescribed in the
2.2 tutorial (which still hasn't changed for 2.3 or 2.4).

Now, classic classes are my habit and I see no compelling reason to
put in the effort to change my habits.

Since the only effort is the addition of

__meta class__ = type

at the head of your modules you could probably automate this without
breaking too much code.

regards
Steve