Re: Struct usages in Python

[Alex Gusarov]

class Event(object):

>
Always subclass object, unless you have a very compelling reason not to,
or you are subclassing something else.
>

I've thought that if I write

class Event:
pass

, it'll be subclass of object too, I was wrong?

--
Best regards, Alex Gusarov

[Diez B. Roggisch]

Re: Struct usages in Python

Alex Gusarov schrieb:

> class Event(object):
>>
>Always subclass object, unless you have a very compelling reason not to,
>or you are subclassing something else.
>>

>
I've thought that if I write
>
class Event:
pass
>
, it'll be subclass of object too, I was wrong?

Yes. That is the somewhat unfortunate difference between new-style and
old-style classes. Use new-style if you can, and that means that
"object" must be part of the inheritance graph.

http://www.cafepy.com/article/python_types_and_objects/python_types_and_objects.html

Diez

[Arnaud Delobelle]

Re: Struct usages in Python

"Alex Gusarov" <alex.m.gusarov @gmail.comwrite s:

> class Event(object):
>>
>Always subclass object, unless you have a very compelling reason not to,
>or you are subclassing something else.
>>

>
I've thought that if I write
>
class Event:
pass
>
, it'll be subclass of object too, I was wrong?

You are wrong for Python 2.X, but right for Python 3 where old-style
classes are gone for good.

What you define with the statement

class Event: pass

is an 'old-style' class. Witness:

>>class Event: pass

...

>>class NewEvent(object ): pass

...

>>type(Event)

<type 'classobj'>

>>type(NewEvent )

<type 'type'>

>>type(Event( ))

<type 'instance'>
del>>type(NewEv ent())
<class '__main__.NewEv ent'>

All old-style classes are actually objects of type 'classobj' (they
all have the same type!), all their instances are all of type 'instance'.

>>type(FooBar ) == type(Event)

True

>>type(FooBar() ) == type(Event())

True

Whereas instances of new-style classes are of type their class:

>>class NewFooBar(objec t): pass

...

>>type(NewFooBa r) == type(NewEvent)

True

>>type(NewFooBa r()) == type(NewEvent() )

False

However, in python 2.X (X 2?), you can force all classes to of a
certain type by setting the global variable '__metaclass__' . So:

>>type(Event) # Event is an old-style class

<type 'classobj'>

>>__metaclass __ = type
>>class Event: pass

...

>>type(Event) # Now Event is new-style!

<type 'type'>

HTH

--
Arnaud

[Arnaud Delobelle]

Re: Struct usages in Python

Arnaud Delobelle <arnodel@google mail.comwrites:

"Alex Gusarov" <alex.m.gusarov @gmail.comwrite s:
>

>> class Event(object):
>>>
>>Always subclass object, unless you have a very compelling reason not to,
>>or you are subclassing something else.
>>>

>>
>I've thought that if I write
>>
>class Event:
> pass
>>
>, it'll be subclass of object too, I was wrong?

>
You are wrong for Python 2.X, but right for Python 3 where old-style
classes are gone for good.
>
What you define with the statement
>
class Event: pass
>
is an 'old-style' class. Witness:
>

>>class Event: pass

...

>>class NewEvent(object ): pass

...

>>type(Event)

<type 'classobj'>

>>type(NewEvent )

<type 'type'>

>>type(Event( ))

<type 'instance'>
del>>type(NewEv ent())
<class '__main__.NewEv ent'>
>
All old-style classes are actually objects of type 'classobj' (they
all have the same type!), all their instances are all of type 'instance'.

Oops somthing disappeared in the copy/paste process:

>>class FooBar: pass

...

>>type(FooBar ) == type(Event)

True

>>type(FooBar() ) == type(Event())

True
>
Whereas instances of new-style classes are of type their class:
>

>>class NewFooBar(objec t): pass

...

>>type(NewFooBa r) == type(NewEvent)

True

>>type(NewFooBa r()) == type(NewEvent() )

False
>
However, in python 2.X (X 2?), you can force all classes to of a
certain type by setting the global variable '__metaclass__' . So:
>

>>type(Event) # Event is an old-style class

<type 'classobj'>

>>__metaclass __ = type
>>class Event: pass

...

>>type(Event) # Now Event is new-style!

<type 'type'>
>
HTH
>
--
Arnaud

[Alex Gusarov]

Re: Struct usages in Python

Yes. That is the somewhat unfortunate difference between new-style and old-style classes.

Use new-style if you can, and that means that "object" must be part of the inheritance graph.

....

You are wrong for Python 2.X, but right for Python 3 where old-style
>
classes are gone for good.

Thanks, I don't knew it before and it's a sensitive information for me.

--
Best regards, Alex Gusarov