Initializing an attribute that needs the object

[David Pratt]

Hi. I want to have different handlers to do perform logic. The problem
is the Handler requires an instance of the factory since it will use its
own methods in conjunction with methods of the factory.

Once I have got a Factory instance I can give it a new handler (see
below). It would be more flexible if I could provide a handle in
constructor - but how to do this when it requires the object itself.
Would I use a super for this sort of thing? Many thanks

Regards,
David


class Factory:

def __init__(self):
self.some_handl er = Handler(self)

f = Factory()
f.some_handler = AnotherHandler( f)

[Bruno Desthuilliers]

Re: Initializing an attribute that needs the object

David Pratt a écrit :[color=blue]
> Hi. I want to have different handlers to do perform logic. The problem
> is the Handler requires an instance of the factory since it will use its
> own methods in conjunction with methods of the factory.
>
> Once I have got a Factory instance I can give it a new handler (see
> below). It would be more flexible if I could provide a handle in
> constructor - but how to do this when it requires the object itself.[/color]

Hint : Python classes are objects too.
[color=blue]
> class Factory:[/color]

Do yourself a favour : use new-style classes.

class Factory(object) :
def __init__(self, handler_class):
self.handler = handler_class(s elf)

class SomeHandler(obj ect):
def __init__(self, factory):
self.factory = factory

f = Factory(SomeHan dler)

[David Pratt]

Re: Initializing an attribute that needs the object

Hi Bruno. This is certainly what I was missing. Thank you. I am afraid I
am behind the times with use of object. Will I only use object when I am
not subclassing? Where will I find a document that provides info on the
use of object in new style classes? Many thanks.

Regards,
David

Bruno Desthuilliers wrote:[color=blue]
> David Pratt a écrit :[color=green]
>> Hi. I want to have different handlers to do perform logic. The problem
>> is the Handler requires an instance of the factory since it will use its
>> own methods in conjunction with methods of the factory.
>>
>> Once I have got a Factory instance I can give it a new handler (see
>> below). It would be more flexible if I could provide a handle in
>> constructor - but how to do this when it requires the object itself.[/color]
>
> Hint : Python classes are objects too.
>[color=green]
>> class Factory:[/color]
>
> Do yourself a favour : use new-style classes.
>
> class Factory(object) :
> def __init__(self, handler_class):
> self.handler = handler_class(s elf)
>
> class SomeHandler(obj ect):
> def __init__(self, factory):
> self.factory = factory
>
> f = Factory(SomeHan dler)[/color]

[John Machin]

Re: Initializing an attribute that needs the object

On 3/06/2006 9:17 AM, David Pratt **TOPPOSTED**:[color=blue]
> Hi Bruno. This is certainly what I was missing. Thank you. I am afraid I
> am behind the times with use of object. Will I only use object when I am
> not subclassing?[/color]

More precisely, don't use object when you are subclassing.
[color=blue]
> Where will I find a document that provides info on the
> use of object in new style classes?
>[/color]

Other way up :-)
A new-style class is one which inherits ultimately from the type that is
called "object".

class NewStyleClass(o bject):
pass

class OldStyleClass() :
pass

Docs are a bit ummmm ...
See this: http://www.python.org/doc/newstyle/

HTH,
John

[David Pratt]

Re: Initializing an attribute that needs the object

Hi John. Thank you for the tips and the link. This is helpful. Many thanks.

Regards
David

[color=blue]
> A new-style class is one which inherits ultimately from the type that is
> called "object".
>
> class NewStyleClass(o bject):
> pass
>
> class OldStyleClass() :
> pass
>
> Docs are a bit ummmm ...
> See this: http://www.python.org/doc/newstyle/
>
> HTH,
> John
>[/color]

[Bruno Desthuilliers]

Re: Initializing an attribute that needs the object

David Pratt a écrit :
<meta>
David, please, don't top-post (fixed)
</meta>[color=blue]
>
> Bruno Desthuilliers wrote:
>[/color]
(snip)[color=blue][color=green]
>>
>> Hint : Python classes are objects too.
>>
>>
>> class Factory(object) :
>> def __init__(self, handler_class):
>> self.handler = handler_class(s elf)
>>
>> class SomeHandler(obj ect):
>> def __init__(self, factory):
>> self.factory = factory
>>
>> f = Factory(SomeHan dler)[/color][/color]
[color=blue]
> Hi Bruno. This is certainly what I was missing. Thank you. I am afraid I
> am behind the times with use of object. Will I only use object when I am
> not subclassing?[/color]

If you subclass from a new-style class (almost all classes in the
standard lib are...), you don't need to anything more.Else, yes, inherit
from 'object', or set 'type' as the metaclass. Both classes defined
below are 'new-style' classes:

class Parrot:
__metaclass__ = type

class CheeseChop(obje ct):
pass


And now:

class DeadParrot(Parr ot):
pass

is a new-style class too.

[color=blue]
> Where will I find a document that provides info on the
> use of object in new style classes?[/color]

In the Fine Manual(tm), of course. Googling python.org for "type
unification" or "new-style" should give relevant answers.