New-style classes questions

[Kalle Anke]

I'm confused by the concepts of old-style vs new-style classes, I've read
most of the documents I found about this but it doesn't "click". Probably
because I wasn't around before 2.2.

Anyway, the reason for new style classes are to make the whole type/object
thing work better together. There are a number of new features etc.

I think my problem is when new-style classes are used, at first I thought
that all classes become new-style classes when I was using 2.4, but if I
understand things correctly I need to subclass an existing class (assuming
that this class does the same) for it to become a new-style class.

Have I understood this correctly?

If I have, then I've got the following question:
=============== =============== =============== ===
Then I could write:

class Foo( Object )

to make a new-style class, and

class FooA

to make an old-style class.
What is the reason for allowing both styles? (backwards compatibility?? )

When I make my own classes should they always be new-style objects or are
there reasons for using old-style object?
=============== =============== =============== ===

[Diez B. Roggisch]

> What is the reason for allowing both styles? (backwards compatibility?? )

yes.

When I make my own classes should they always be new-style objects or are
there reasons for using old-style object?

No, use new style if you can - except from the rare cases where above
mentioned backwards compatibilty is needed. E.g. exceptions have to be
old-style, and for example omniorb needs old-style classes for corba
implementations .

Diez

[Gerrit Holl]

Diez B. Roggisch wrote:

What is the reason for allowing both styles? (backwards compatibility?? )

yes.

Note that there is another way to create new-style classes:

__metaclass__ = type

before the first class definition:

class Foo: pass .... type(Foo) <type 'classobj'> __metaclass__ = type
class Bar: pass .... type(Bar)

<type 'type'>

I like this. However, perhaps other people reading my source code won't
like it, because when they see 'class Foo:', they might expect an
old-style class. But it's so much better to type and to read, that I
prefer this.

Does the Python style guide have any severe penalty for using this?

regards,
Gerrit.

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[Kalle Anke]

On Sun, 25 Sep 2005 15:24:29 +0200, Gerrit Holl wrote
(in article <ma************ *************** *********@pytho n.org>):

I like this. However, perhaps other people reading my source code won't
like it, because when they see 'class Foo:', they might expect an
old-style class. But it's so much better to type and to read, that I
prefer this.
I personally would find this more difficult to read but it's a matter of
taste I suppose.
Det finns inte dåligt väder, bara dåliga kläder.

Så sant som det var sagt
jem